Fix nullability errors.

Radzen.Blazor.Tests/PagerTests.cs

@@ -2,7 +2,6 @@ using Bunit;
 using Bunit.JSInterop;
 using System;
 using System.Collections.Generic;
-using System.Threading.Tasks;
 using Xunit;
 
 namespace Radzen.Blazor.Tests
@@ -55,7 +54,7 @@ namespace Radzen.Blazor.Tests
         }
 
         [Fact]
-        public async Task RadzenPager_Renders_Summary() {
+        public async void RadzenPager_Renders_Summary() {
             using var ctx = new TestContext();
             ctx.JSInterop.Mode = JSRuntimeMode.Loose;
             ctx.JSInterop.SetupModule("_content/Radzen.Blazor/Radzen.Blazor.js");
@@ -65,7 +64,7 @@ namespace Radzen.Blazor.Tests
                 parameters.Add<int>(p => p.Count, 100);
                 parameters.Add<bool>(p => p.ShowPagingSummary, true);
             });
-            await component.InvokeAsync(() => component.Instance.GoToPage(2));
+            await component.Instance.GoToPage(2);
             component.Render();
 
             Assert.Contains(@$"rz-pager-summary", component.Markup); 
@@ -112,7 +111,7 @@ namespace Radzen.Blazor.Tests
         }
 
         [Fact]
-        public async Task RadzenPager_First_And_Prev_Buttons_Are_Disabled_When_On_The_First_Page()
+        public async void RadzenPager_First_And_Prev_Buttons_Are_Disabled_When_On_The_First_Page()
         {
             using var ctx = new TestContext();
             ctx.JSInterop.Mode = JSRuntimeMode.Loose;
@@ -124,7 +123,7 @@ namespace Radzen.Blazor.Tests
                 parameters.Add<bool>(p => p.ShowPagingSummary, true);
             });
 
-            await component.InvokeAsync(() => component.Instance.GoToPage(0));
+            await component.Instance.GoToPage(0);
             component.Render();
 
             var firstPageButton = component.Find("a.rz-pager-first");
@@ -135,7 +134,7 @@ namespace Radzen.Blazor.Tests
         }
 
         [Fact]
-        public async Task RadzenPager_Last_And_Next_Buttons_Are_Disabled_When_On_The_Last_Page()
+        public async void RadzenPager_Last_And_Next_Buttons_Are_Disabled_When_On_The_Last_Page()
         {
             using var ctx = new TestContext();
             ctx.JSInterop.Mode = JSRuntimeMode.Loose;
@@ -147,7 +146,7 @@ namespace Radzen.Blazor.Tests
                 parameters.Add<bool>(p => p.ShowPagingSummary, true);
             });
 
-            await component.InvokeAsync(() => component.Instance.GoToPage(9));
+            await component.Instance.GoToPage(9);
             component.Render();
 
             var lastPageButton = component.Find("a.rz-pager-last");

Radzen.Blazor.Tests/PropertyAccessTests.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using Xunit;
 
@@ -114,11 +114,6 @@ namespace Radzen.Blazor.Tests
             public List<string> Values { get; set; }
         }
 
-        public class Order
-        {
-            public DateTime? OrderDate { get; set; }
-        }
-
         [Fact]
         public void GetProperty_Should_Resolve_DescriptionProperty()
         {
@@ -142,14 +137,6 @@ namespace Radzen.Blazor.Tests
             Assert.NotNull(idProperty);
         }
 
-        [Fact]
-        public void GetPropertyType_Resolves_NullableDateTime_Date()
-        {
-            var propertyType = PropertyAccess.GetPropertyType(typeof(Order), "OrderDate.Date");
-
-            Assert.Equal(typeof(DateTime), propertyType);
-        }
-
         interface ISimpleInterface : ISimpleNestedInterface
         {
             string Description { get; set; }

Radzen.Blazor.Tests/QueryableExtensionTests.cs

@@ -3,7 +3,6 @@ using System.Collections.Generic;
 using System.Linq;
 using Xunit;
 using Radzen;
-using System.Linq.Expressions;
 
 namespace Radzen.Blazor.Tests
 {
@@ -25,11 +24,6 @@ namespace Radzen.Blazor.Tests
             public int Priority { get; set; }
         }
 
-        private class Order
-        {
-            public DateTime? OrderDate { get; set; }
-        }
-
         private List<TestItem> GetTestData()
         {
             return new List<TestItem>
@@ -42,24 +36,6 @@ namespace Radzen.Blazor.Tests
             };
         }
 
-        [Fact]
-        public void GetNestedPropertyExpression_Handles_NullableDateTime_Date()
-        {
-            var parameter = Expression.Parameter(typeof(Order), "x");
-            var expression = QueryableExtension.GetNestedPropertyExpression(parameter, "OrderDate.Date");
-            var getter = Expression.Lambda<Func<Order, DateTime>>(expression, parameter).Compile();
-
-            var order = new Order { OrderDate = new DateTime(2024, 2, 3, 14, 30, 0) };
-            var result = getter(order);
-
-            Assert.Equal(order.OrderDate.Value.Date, result);
-
-            var nullOrder = new Order { OrderDate = null };
-            var nullResult = getter(nullOrder);
-
-            Assert.Equal(default(DateTime), nullResult);
-        }
-
         // OrderBy tests
         [Fact]
         public void OrderBy_SortsAscending_ByDefault()
@@ -352,7 +328,7 @@ namespace Radzen.Blazor.Tests
             
             var result = data.Where(filters, LogicalFilterOperator.And, FilterCaseSensitivity.Default).ToList();
             
-            Assert.Equal(1, result.Count);
+            Assert.Single(result);
             Assert.Equal("Eve", result[0].Name);
         }
 

Radzen.Blazor.Tests/Spreadsheet/AggregateFunctionTests.cs

@@ -0,0 +1,49 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class AggregateFunctionTests
+{
+    readonly Sheet sheet = new(15, 5);
+
+    void SeedWithErrors()
+    {
+        sheet.Cells["A1"].Formula = "=A2/0"; // #DIV/0!
+        sheet.Cells["A2"].Value = 82;
+        sheet.Cells["A3"].Value = 72;
+        sheet.Cells["A4"].Value = 65;
+        sheet.Cells["A5"].Value = 30;
+        sheet.Cells["A6"].Value = 95;
+        sheet.Cells["A7"].Formula = "=0/0"; // #DIV/0!
+        sheet.Cells["A8"].Value = 63;
+        sheet.Cells["A9"].Value = 31;
+        sheet.Cells["A10"].Value = 53;
+        sheet.Cells["A11"].Value = 96;
+    }
+
+    [Fact]
+    public void ShouldComputeMaxIgnoringErrors()
+    {
+        SeedWithErrors();
+        sheet.Cells["B1"].Formula = "=AGGREGATE(4,6,A1:A11)"; // MAX ignoring errors
+        Assert.Equal(96d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldComputeLargeIgnoringErrors()
+    {
+        SeedWithErrors();
+        sheet.Cells["B1"].Formula = "=AGGREGATE(14,6,A1:A11,3)"; // LARGE k=3 ignoring errors
+        Assert.Equal(82d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorWhenKMissingForSmall()
+    {
+        SeedWithErrors();
+        sheet.Cells["B1"].Formula = "=AGGREGATE(15,6,A1:A11)"; // SMALL requires k
+        Assert.Equal(CellError.Value, sheet.Cells["B1"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/AndFunctionTests.cs

@@ -0,0 +1,160 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class AndFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithAllTrueValues()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Value = true;
+        sheet.Cells["A3"].Formula = "=AND(A1,A2)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithOneFalseValue()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Formula = "=AND(A1,A2)";
+
+        Assert.Equal(false, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithAllFalseValues()
+    {
+        sheet.Cells["A1"].Value = false;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Formula = "=AND(A1,A2)";
+
+        Assert.Equal(false, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithNumericValues()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Value = 10;
+        sheet.Cells["A3"].Formula = "=AND(A1>1,A2<100)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithZeroAsFalse()
+    {
+        sheet.Cells["A1"].Value = 0;
+        sheet.Cells["A2"].Value = 1;
+        sheet.Cells["A3"].Formula = "=AND(A1,A2)";
+
+        Assert.Equal(false, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithNonZeroAsTrue()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Value = 10;
+        sheet.Cells["A3"].Formula = "=AND(A1,A2)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithStringValues()
+    {
+        sheet.Cells["A1"].Value = "test";
+        sheet.Cells["A2"].Value = "hello";
+        sheet.Cells["A3"].Formula = "=AND(A1,A2)";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithEmptyStringAsFalse()
+    {
+        sheet.Cells["A2"].Value = "hello";
+        sheet.Cells["A3"].Formula = "=AND(A1,A2)";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithMultipleArguments()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Value = true;
+        sheet.Cells["A3"].Value = true;
+        sheet.Cells["A4"].Formula = "=AND(A1,A2,A3)";
+
+        Assert.Equal(true, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithOneFalseInMultipleArguments()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Value = true;
+        sheet.Cells["A4"].Formula = "=AND(A1,A2,A3)";
+
+        Assert.Equal(false, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForEmptyAndFunction()
+    {
+        sheet.Cells["A1"].Formula = "=AND()";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithRangeExpression()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Value = true;
+        sheet.Cells["A3"].Formula = "=AND(A1:A2)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionWithMixedTypes()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Value = "3";
+        sheet.Cells["A3"].Value = true;
+        sheet.Cells["A4"].Formula = "=AND(A1,A2,A3)";
+
+        Assert.Equal(true, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionInIfStatement()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Value = 10;
+        sheet.Cells["A3"].Formula = "=IF(AND(A1>1,A2<100),A1,\"Out of range\")";
+
+        Assert.Equal(5d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionInIfStatementWithFalseCondition()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Value = 150;
+        sheet.Cells["A3"].Formula = "=IF(AND(A1>1,A2<100),A1,\"Out of range\")";
+
+        Assert.Equal("Out of range", sheet.Cells["A3"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/AutoFilterTests.cs

@@ -0,0 +1,105 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class AutoFilterTests
+{
+    private readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void Should_ToggleSheetAutoFilter()
+    {
+        // Initially no auto filter
+        Assert.Null(sheet.AutoFilter);
+
+        // Apply auto filter to range A1:C5
+        var range = RangeRef.Parse("A1:C5");
+        var command = new SheetAutoFilterCommand(sheet, range);
+        command.Execute();
+
+        // Auto filter should be applied
+        Assert.NotNull(sheet.AutoFilter);
+        Assert.Equal(range, sheet.AutoFilter.Range);
+
+        // Undo the command
+        command.Unexecute();
+
+        // Auto filter should be removed
+        Assert.Null(sheet.AutoFilter);
+    }
+
+    [Fact]
+    public void Should_ToggleDataTableFilterButton()
+    {
+        // Add a data table
+        var range = RangeRef.Parse("A1:C5");
+        sheet.AddTable(range);
+
+        var table = sheet.Tables[0];
+        
+        // Initially ShowFilterButton should be true
+        Assert.True(table.ShowFilterButton);
+
+        // Toggle filter button off
+        var command = new TableFilterCommand(sheet, 0);
+        command.Execute();
+
+        // ShowFilterButton should be false
+        Assert.False(table.ShowFilterButton);
+
+        // Undo the command
+        command.Unexecute();
+
+        // ShowFilterButton should be true again
+        Assert.True(table.ShowFilterButton);
+    }
+
+    [Fact]
+    public void Should_HandleMultipleDataTables()
+    {
+        // Add two data tables
+        sheet.AddTable(RangeRef.Parse("A1:C5"));
+        sheet.AddTable(RangeRef.Parse("E1:G5"));
+
+        var table1 = sheet.Tables[0];
+        var table2 = sheet.Tables[1];
+
+        // Initially both should have ShowFilterButton = true
+        Assert.True(table1.ShowFilterButton);
+        Assert.True(table2.ShowFilterButton);
+
+        // Toggle filter button for first data table
+        var command1 = new TableFilterCommand(sheet, 0);
+        command1.Execute();
+
+        // Only first data table should be affected
+        Assert.False(table1.ShowFilterButton);
+        Assert.True(table2.ShowFilterButton);
+
+        // Toggle filter button for second data table
+        var command2 = new TableFilterCommand(sheet, 1);
+        command2.Execute();
+
+        // Both should be affected
+        Assert.False(table1.ShowFilterButton);
+        Assert.False(table2.ShowFilterButton);
+
+        // Undo second command
+        command2.Unexecute();
+
+        // Only second data table should be restored
+        Assert.False(table1.ShowFilterButton);
+        Assert.True(table2.ShowFilterButton);
+    }
+
+    [Fact]
+    public void Should_HandleInvalidDataTableIndex()
+    {
+        // Try to toggle filter button for non-existent data table
+        var command = new TableFilterCommand(sheet, 0);
+        
+        // Should not throw exception
+        var result = command.Execute();
+        Assert.True(result);
+    }
+} 

Radzen.Blazor.Tests/Spreadsheet/AverageFunctionTests.cs

@@ -0,0 +1,114 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class AverageFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void ShouldEvaluateAverageFunctionWithTwoArguments()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15;
+        sheet.Cells["A3"].Formula = "=AVERAGE(A1,A2)";
+
+        Assert.Equal(12.5, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAverageFunctionWithEmptyCells()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A3"].Formula = "=AVERAGE(A1,A2)";
+
+        Assert.Equal(10.0, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAverageFunctionWithMultipleArguments()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15;
+        sheet.Cells["A3"].Value = 20;
+        sheet.Cells["A4"].Formula = "=AVERAGE(A1,A2,A3)";
+
+        Assert.Equal(15.0, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnDiv0ErrorForEmptyAverageFunction()
+    {
+        sheet.Cells["A1"].Formula = "=AVERAGE()";
+
+        Assert.Equal(CellError.Div0, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnDiv0ErrorForAverageFunctionWithNoNumericValues()
+    {
+        sheet.Cells["A1"].Value = "text";
+        sheet.Cells["A2"].Value = "";
+        sheet.Cells["A3"].Formula = "=AVERAGE(A1,A2)";
+
+        Assert.Equal(CellError.Div0, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAverageFunctionWithRange()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15;
+        sheet.Cells["A3"].Formula = "=AVERAGE(A1:A2)";
+
+        Assert.Equal(12.5, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAverageFunctionWithMixedTypes()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15.5;
+        sheet.Cells["A3"].Formula = "=AVERAGE(A1,A2)";
+
+        Assert.Equal(12.75, sheet.Cells["A3"].Value);
+
+        sheet.Cells["A4"].Value = 2.5;
+        sheet.Cells["A5"].Formula = "=AVERAGE(A4,A1)";
+
+        Assert.Equal(6.25, sheet.Cells["A5"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAverageFunctionIgnoringTextAndLogicalValues()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "text";
+        sheet.Cells["A3"].Value = true;
+        sheet.Cells["A4"].Value = 20;
+        sheet.Cells["A5"].Formula = "=AVERAGE(A1,A2,A3,A4)";
+
+        Assert.Equal(15.0, sheet.Cells["A5"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAverageFunctionIncludingZeroValues()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 0;
+        sheet.Cells["A3"].Value = 20;
+        sheet.Cells["A4"].Formula = "=AVERAGE(A1,A2,A3)";
+
+        Assert.Equal(10.0, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldCreateRefErrorWhenAverageRangeOutOfBounds()
+    {
+        sheet.Cells["A1"].Formula = "=AVERAGE(A2:A6)";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["A1"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/CellSelectionTests.cs

@@ -0,0 +1,261 @@
+using Bunit;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class CellSelectionTests : TestContext
+{
+    private readonly Sheet sheet = new (4,4);
+
+    [Fact]
+    public void CellSelection_RendersWithCorrectClasses()
+    {
+        // Arrange
+        var cell = new CellRef(0, 0);
+        sheet.Selection.Select(new RangeRef(cell, cell));
+        var context = new MockVirtualGridContext();
+
+        // Act
+        var cut = RenderComponent<CellSelection>(parameters => parameters
+            .Add(p => p.Cell, cell)
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Context, context));
+
+        // Assert
+        var element = cut.Find(".rz-spreadsheet-selection-cell");
+        Assert.NotNull(element);
+        Assert.Contains("rz-spreadsheet-selection-cell", element.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-top", element.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-left", element.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-bottom", element.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-right", element.ClassName);
+    }
+
+    [Fact]
+    public void CellSelection_AppliesFrozenColumnClass()
+    {
+        // Arrange
+        var cell = new CellRef(0, 0);
+        sheet.Columns.Frozen = 1;
+        sheet.Selection.Select(new RangeRef(cell, cell));
+        var context = new MockVirtualGridContext();
+
+        // Act
+        var cut = RenderComponent<CellSelection>(parameters => parameters
+            .Add(p => p.Cell, cell)
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Context, context));
+
+        // Assert
+        var element = cut.Find(".rz-spreadsheet-selection-cell");
+        Assert.Contains("rz-spreadsheet-frozen-column", element.ClassName);
+    }
+
+    [Fact]
+    public void CellSelection_AppliesFrozenRowClass()
+    {
+        // Arrange
+        var cell = new CellRef(0, 0);
+        var context = new MockVirtualGridContext();
+        sheet.Rows.Frozen = 1;
+        sheet.Selection.Select(new RangeRef(cell, cell));
+
+        // Act
+        var cut = RenderComponent<CellSelection>(parameters => parameters
+            .Add(p => p.Cell, cell)
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Context, context));
+
+        // Assert
+        var element = cut.Find(".rz-spreadsheet-selection-cell");
+        Assert.Contains("rz-spreadsheet-frozen-row", element.ClassName);
+    }
+
+    [Fact]
+    public void CellSelection_CalculatesStyle()
+    {
+        // Arrange
+        var cell = new CellRef(0, 0);
+        sheet.Selection.Select(new RangeRef(cell, cell));
+        var context = new MockVirtualGridContext();
+
+        // Act
+        var cut = RenderComponent<CellSelection>(parameters => parameters
+            .Add(p => p.Cell, cell)
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Context, context));
+
+        // Assert
+        var element = cut.Find(".rz-spreadsheet-selection-cell");
+        Assert.Equal("transform: translate(0px, 0px); width: 100px; height: 24px", element.GetAttribute("style"));
+    }
+
+    [Fact]
+    public void CellSelection_SplitsMergedCell_WhenIntersectingFrozenRow()
+    {
+        // Arrange
+        sheet.Rows.Frozen = 1;
+        var range = new RangeRef(new CellRef(0, 0), new CellRef(2, 0));
+        sheet.MergedCells.Add(range);
+        sheet.Selection.Select(range);
+        var context = new MockVirtualGridContext();
+
+        // Act
+        var cut = RenderComponent<CellSelection>(parameters => parameters
+            .Add(p => p.Cell, new CellRef(0, 0))
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Context, context));
+
+        // Assert
+        var elements = cut.FindAll(".rz-spreadsheet-selection-cell");
+        Assert.Equal(2, elements.Count);
+
+        var frozen = cut.Find(".rz-spreadsheet-frozen-row");
+
+        Assert.NotNull(frozen);
+        
+        // First element (frozen)
+        Assert.Equal("transform: translate(0px, 0px); width: 100px; height: 24px", frozen.GetAttribute("style"));
+        Assert.Contains("rz-spreadsheet-selection-cell-top", frozen.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-left", frozen.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-right", frozen.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-bottom", frozen.ClassName);
+
+        var unfrozen = elements.Where(e => e != frozen).FirstOrDefault();
+
+        Assert.NotNull(unfrozen);
+        
+        // Second element (non-frozen)
+        Assert.Equal("transform: translate(0px, 24px); width: 100px; height: 48px", unfrozen.GetAttribute("style"));
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-top", unfrozen.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-left", unfrozen.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-right", unfrozen.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-bottom", unfrozen.ClassName);
+    }
+
+    [Fact]
+    public void CellSelection_SplitsMergedCell_WhenIntersectingFrozenColumn()
+    {
+        // Arrange
+        sheet.Columns.Frozen = 1;
+        var range = new RangeRef(new CellRef(0, 0), new CellRef(0, 2));
+        sheet.MergedCells.Add(range);
+        sheet.Selection.Select(range);
+        var context = new MockVirtualGridContext();
+
+        // Act
+        var cut = RenderComponent<CellSelection>(parameters => parameters
+            .Add(p => p.Cell, new CellRef(0, 0))
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Context, context));
+
+        // Assert
+        var elements = cut.FindAll(".rz-spreadsheet-selection-cell");
+        Assert.Equal(2, elements.Count);
+
+        var frozen = cut.Find(".rz-spreadsheet-frozen-column");
+
+        Assert.NotNull(frozen);
+        
+        // First element (frozen)
+        Assert.Contains("rz-spreadsheet-frozen-column", frozen.ClassName);
+        Assert.Equal("transform: translate(0px, 0px); width: 100px; height: 24px", frozen.GetAttribute("style"));
+        Assert.Contains("rz-spreadsheet-selection-cell-top", frozen.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-left", frozen.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-bottom", frozen.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-right", frozen.ClassName);
+        
+        var unfrozen = elements.Where(e => e != frozen).FirstOrDefault();
+
+        Assert.NotNull(unfrozen);
+        // Second element (non-frozen)
+        Assert.Equal("transform: translate(100px, 0px); width: 200px; height: 24px", unfrozen.GetAttribute("style"));
+        Assert.Contains("rz-spreadsheet-selection-cell-top", unfrozen.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-left", unfrozen.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-bottom", unfrozen.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-right", unfrozen.ClassName);
+    }
+
+    [Fact]
+    public void CellSelection_SplitsMergedCell_WhenIntersectingBothFrozen()
+    {
+        // Arrange
+        sheet.Rows.Frozen = 1;
+        sheet.Columns.Frozen = 1;
+        var range = new RangeRef(new CellRef(0, 0), new CellRef(2, 2));
+        sheet.MergedCells.Add(range);
+        sheet.Selection.Select(range);
+        var context = new MockVirtualGridContext();
+
+        // Act
+        var cut = RenderComponent<CellSelection>(parameters => parameters
+            .Add(p => p.Cell, new CellRef(0, 0))
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Context, context));
+
+        // Assert
+        var elements = cut.FindAll(".rz-spreadsheet-selection-cell");
+        Assert.Equal(4, elements.Count);
+
+        // Top-left element (both frozen)
+        var both = cut.Find(".rz-spreadsheet-frozen-row.rz-spreadsheet-frozen-column");
+        Assert.NotNull(both);
+        Assert.Contains("rz-spreadsheet-frozen-row", both.ClassName);
+        Assert.Contains("rz-spreadsheet-frozen-column", both.ClassName);
+        Assert.Equal("transform: translate(0px, 0px); width: 100px; height: 24px", both.GetAttribute("style"));
+        Assert.Contains("rz-spreadsheet-selection-cell-top", both.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-left", both.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-bottom", both.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-right", both.ClassName);
+        
+        // Bottom-left element (column frozen)
+        var frozenColumn = cut.Find(".rz-spreadsheet-frozen-column:not(.rz-spreadsheet-frozen-row)");
+        Assert.NotNull(frozenColumn);
+        Assert.DoesNotContain("rz-spreadsheet-frozen-row", frozenColumn.ClassName);
+        Assert.Contains("rz-spreadsheet-frozen-column", frozenColumn.ClassName);
+        Assert.Equal("transform: translate(0px, 24px); width: 100px; height: 48px", frozenColumn.GetAttribute("style"));
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-top", frozenColumn.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-left", frozenColumn.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-bottom", frozenColumn.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-right", frozenColumn.ClassName);
+        
+        // Top-right element (row frozen)
+        var frozenRow = cut.Find(".rz-spreadsheet-frozen-row:not(.rz-spreadsheet-frozen-column)");
+        Assert.NotNull(frozenRow);
+        Assert.Contains("rz-spreadsheet-frozen-row", frozenRow.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-frozen-column", frozenRow.ClassName);
+        Assert.Equal("transform: translate(100px, 0px); width: 200px; height: 24px", frozenRow.GetAttribute("style"));
+        Assert.Contains("rz-spreadsheet-selection-cell-top", frozenRow.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-left", frozenRow.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-bottom", frozenRow.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-right", frozenRow.ClassName);
+        
+        // Bottom-right element (neither frozen)
+        var neither = elements.FirstOrDefault(e => e != both && e != frozenColumn && e != frozenRow);
+        Assert.NotNull(neither);
+        Assert.DoesNotContain("rz-spreadsheet-frozen-row", neither.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-frozen-column", neither.ClassName);
+        Assert.Equal("transform: translate(100px, 24px); width: 200px; height: 48px", neither.GetAttribute("style"));
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-top", neither.ClassName);
+        Assert.DoesNotContain("rz-spreadsheet-selection-cell-left", neither.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-bottom", neither.ClassName);
+        Assert.Contains("rz-spreadsheet-selection-cell-right", neither.ClassName);
+    }
+}
+
+public class MockVirtualGridContext : IVirtualGridContext
+{
+    private readonly Dictionary<(int Row, int Column), PixelRectangle> rectangle = [];
+
+    public void SetupRectangle(int row, int column, PixelRectangle rectangle)
+    {
+        this.rectangle[(row, column)] = rectangle;
+    }
+
+    public PixelRectangle GetRectangle(int row, int column) => throw new NotImplementedException();
+
+    public PixelRectangle GetRectangle(int top, int left, int bottom, int right) => new(new (left * 100, (right + 1) * 100), new (top*24, (bottom + 1)*24));
+} 

Radzen.Blazor.Tests/Spreadsheet/CellStoreTests.cs

@@ -0,0 +1,69 @@
+using System;
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class CellStoreTests
+{
+    readonly CellStore cellStore = new(new Sheet(5, 5));
+
+    [Fact]
+    public void CellStore_ShouldReturnNewCell_WhenCellDoesNotExist()
+    {
+        var cell = cellStore[0, 0];
+
+        Assert.NotNull(cell);
+    }
+
+    [Fact]
+    public void CellStore_ShouldThrowArgumentOutOfRangeException_WhenRowExceedsMax()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() => cellStore[5, 0]);
+    }
+
+    [Fact]
+    public void CellStore_ShouldThrowArgumentOutOfRangeException_WhenColumnExceedsMax()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() => cellStore[0, 5]);
+    }
+
+    [Fact]
+    public void CellStore_ShouldReturnExistingCell_WhenCellExists()
+    {
+        var expectedCell = new Cell(cellStore.Sheet, new CellRef(0, 0));
+        cellStore[0, 0] = expectedCell;
+        var cell = cellStore[0, 0];
+        Assert.Same(expectedCell, cell);
+    }
+
+    [Fact]
+    public void CellStore_ShouldReturnExistingCell_ViaA1Notation()
+    {
+        var expectedCell = new Cell(cellStore.Sheet, new CellRef(0, 0));
+
+        cellStore[0, 0] = expectedCell;
+
+        var cell = cellStore["A1"];
+
+        Assert.Same(expectedCell, cell);
+    }
+
+    [Fact]
+    public void CellStore_ShouldThrowException_WhenInvalidA1Notation()
+    {
+        Assert.Throws<ArgumentException>(() => cellStore["Invalid"]);
+    }
+
+    [Fact]
+    public void CellStore_ShouldSupport_MultipleLettersInA1Notation()
+    {
+        var cellStore = new CellStore(new Sheet(5, 30));
+        var expectedCell = new Cell(cellStore.Sheet, new CellRef(0, 26));
+
+        cellStore[0, 26] = expectedCell;
+
+        var cell = cellStore["AA1"];
+
+        Assert.Same(expectedCell, cell);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/ChooseFunctionTests.cs

@@ -0,0 +1,34 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class ChooseFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldPickScalarByIndex()
+    {
+        sheet.Cells["A1"].Formula = "=CHOOSE(3,\"Wide\",115,\"world\",8)";
+        Assert.Equal("world", sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldPickCellReferenceByIndex()
+    {
+        sheet.Cells["A2"].Value = "1st";
+        sheet.Cells["A3"].Value = "2nd";
+        sheet.Cells["A4"].Value = "3rd";
+        sheet.Cells["A5"].Value = "Finished";
+
+        sheet.Cells["B1"].Formula = "=CHOOSE(2,A2,A3,A4,A5)";
+        Assert.Equal("2nd", sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorWhenIndexOutOfRange()
+    {
+        sheet.Cells["A1"].Formula = "=CHOOSE(5,1,2,3)";
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/ColumnFunctionTests.cs

@@ -0,0 +1,40 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class ColumnFunctionTests
+{
+    [Fact]
+    public void Column_OmittedReference_ReturnsCurrentColumn()
+    {
+        var sheet = new Sheet(20, 10);
+        sheet.Cells["C10"].Formula = "=COLUMN()";
+        Assert.Equal(3d, sheet.Cells["C10"].Data.Value);
+    }
+
+    [Fact]
+    public void Column_SingleCellReference_ReturnsThatColumn()
+    {
+        var sheet = new Sheet(20, 10);
+        sheet.Cells["A1"].Formula = "=COLUMN(C10)";
+        Assert.Equal(3d, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Column_RangeReference_SingleRow_ReturnsLeftmostColumn()
+    {
+        var sheet = new Sheet(20, 10);
+        sheet.Cells["B2"].Formula = "=COLUMN(C10:E10)";
+        Assert.Equal(3d, sheet.Cells["B2"].Data.Value);
+    }
+
+    [Fact]
+    public void Column_RangeReference_MultiRowAndColumn_IsError()
+    {
+        var sheet = new Sheet(20, 10);
+        sheet.Cells["B2"].Formula = "=COLUMN(C10:D20)";
+        Assert.Equal(CellError.Value, sheet.Cells["B2"].Data.Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/ColumnsFunctionTests.cs

@@ -0,0 +1,30 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class ColumnsFunctionTests
+{
+    [Fact]
+    public void Columns_Range_ReturnsColumnCount()
+    {
+        var sheet = new Sheet(50, 20);
+        sheet.Cells["A1"].Formula = "=COLUMNS(C1:E4)";
+        Assert.Equal(3d, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Columns_SingleCell_ReturnsOne()
+    {
+        var sheet = new Sheet(50, 20);
+        sheet.Cells["A1"].Formula = "=COLUMNS(C10)";
+        Assert.Equal(1d, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Columns_SingleColumnRange_ReturnsOne()
+    {
+        var sheet = new Sheet(50, 20);
+        sheet.Cells["A1"].Formula = "=COLUMNS(C10:C20)";
+        Assert.Equal(1d, sheet.Cells["A1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/ConcatFunctionTests.cs

@@ -0,0 +1,44 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class ConcatFunctionTests
+{
+    [Fact]
+    public void Concat_Literals_Works()
+    {
+        var sheet = new Sheet(20, 10);
+        sheet.Cells["A1"].Formula = "=CONCAT(\"The\",\" \",\"sun\",\" \",\"will\",\" \",\"come\",\" \",\"up\",\" \",\"tomorrow.\")";
+        Assert.Equal("The sun will come up tomorrow.", sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Concat_SingleRange_LinearizesRowMajor()
+    {
+        var sheet = new Sheet(20, 10);
+        sheet.Cells["B2"].Value = "a1";
+        sheet.Cells["C2"].Value = "b1";
+        sheet.Cells["B3"].Value = "a2";
+        sheet.Cells["C3"].Value = "b2";
+        sheet.Cells["B4"].Value = "a4";
+        sheet.Cells["C4"].Value = "b4";
+        sheet.Cells["B5"].Value = "a5";
+        sheet.Cells["C5"].Value = "b5";
+        sheet.Cells["B6"].Value = "a6";
+        sheet.Cells["C6"].Value = "b6";
+        sheet.Cells["B7"].Value = "a7";
+        sheet.Cells["C7"].Value = "b7";
+        sheet.Cells["A1"].Formula = "=CONCAT(B2:C7)";
+        Assert.Equal("a1b1a2b2a4b4a5b5a6b6a7b7", sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Concat_MixedArgs_RangeAndLiterals()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["B2"].Value = "Andreas";
+        sheet.Cells["C2"].Value = "Hauser";
+        sheet.Cells["A1"].Formula = "=CONCAT(B2,\" \",C2)";
+        Assert.Equal("Andreas Hauser", sheet.Cells["A1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/CountAllFunctionTests.cs

@@ -0,0 +1,150 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class CountAllFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void ShouldEvaluateCountaFunctionWithTwoArguments()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15;
+        sheet.Cells["A3"].Formula = "=COUNTA(A1,A2)";
+
+        Assert.Equal(2.0, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountaFunctionWithEmptyCells()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A3"].Formula = "=COUNTA(A1,A2)";
+
+        Assert.Equal(1.0, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountaFunctionWithMultipleArguments()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15;
+        sheet.Cells["A3"].Value = 20;
+        sheet.Cells["A4"].Formula = "=COUNTA(A1,A2,A3)";
+
+        Assert.Equal(3.0, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnZeroForEmptyCountaFunction()
+    {
+        sheet.Cells["A1"].Formula = "=COUNTA()";
+
+        Assert.Equal(0.0, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountaFunctionWithRange()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15;
+        sheet.Cells["A3"].Formula = "=COUNTA(A1:A2)";
+
+        Assert.Equal(2.0, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountaFunctionIncludingTextValues()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "text";
+        sheet.Cells["A3"].Value = 20;
+        sheet.Cells["A4"].Formula = "=COUNTA(A1,A2,A3)";
+
+        Assert.Equal(3.0, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountaFunctionIncludingLogicalValues()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = true;
+        sheet.Cells["A3"].Value = false;
+        sheet.Cells["A4"].Value = 20;
+        sheet.Cells["A5"].Formula = "=COUNTA(A1,A2,A3,A4)";
+
+        Assert.Equal(4.0, sheet.Cells["A5"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountaFunctionIncludingEmptyStrings()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "";
+        sheet.Cells["A3"].Value = 20;
+        sheet.Cells["A4"].Formula = "=COUNTA(A1,A2,A3)";
+
+        Assert.Equal(3.0, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountaFunctionIgnoringTrulyEmptyCells()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "text";
+        sheet.Cells["A4"].Value = 20;
+        sheet.Cells["A5"].Formula = "=COUNTA(A1,A2,A3,A4)";
+
+        Assert.Equal(3.0, sheet.Cells["A5"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountaFunctionWithAllNumericValues()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+        sheet.Cells["A4"].Formula = "=COUNTA(A1,A2,A3)";
+
+        Assert.Equal(3.0, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldShowDifferenceBetweenCountAndCounta()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "text";
+        sheet.Cells["A3"].Value = true;
+        sheet.Cells["A4"].Value = "";
+        sheet.Cells["A5"].Value = 20;
+        sheet.Cells["B1"].Formula = "=COUNT(A1,A2,A3,A4,A5)";
+        sheet.Cells["B2"].Formula = "=COUNTA(A1,A2,A3,A4,A5)";
+
+        Assert.Equal(3.0, sheet.Cells["B1"].Value);
+        Assert.Equal(5.0, sheet.Cells["B2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountaFunctionWithMixedTypes()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "text";
+        sheet.Cells["A3"].Value = true;
+        sheet.Cells["A4"].Value = "";
+        sheet.Cells["A5"].Value = 3.14;
+        sheet.Cells["B1"].Formula = "=COUNTA(A1,A2,A3,A4,A5)";
+
+        Assert.Equal(5.0, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldCreateRefErrorWhenCountaRangeOutOfBounds()
+    {
+        sheet.Cells["A1"].Formula = "=COUNTA(A2:A6)";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["A1"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/CountFunctionTests.cs

@@ -0,0 +1,139 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class CountFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void ShouldEvaluateCountFunctionWithTwoArguments()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15;
+        sheet.Cells["A3"].Formula = "=COUNT(A1,A2)";
+
+        Assert.Equal(2.0, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountFunctionWithEmptyCells()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A3"].Formula = "=COUNT(A1,A2)";
+
+        Assert.Equal(1.0, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountFunctionWithMultipleArguments()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15;
+        sheet.Cells["A3"].Value = 20;
+        sheet.Cells["A4"].Formula = "=COUNT(A1,A2,A3)";
+
+        Assert.Equal(3.0, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnZeroForEmptyCountFunction()
+    {
+        sheet.Cells["A1"].Formula = "=COUNT()";
+
+        Assert.Equal(0.0, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountFunctionWithRange()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15;
+        sheet.Cells["A3"].Formula = "=COUNT(A1:A2)";
+
+        Assert.Equal(2.0, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountFunctionWithMixedTypes()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 15.5;
+        sheet.Cells["A3"].Formula = "=COUNT(A1,A2)";
+
+        Assert.Equal(2.0, sheet.Cells["A3"].Value);
+
+        sheet.Cells["A4"].Value = 2.5;
+        sheet.Cells["A5"].Formula = "=COUNT(A4,A1)";
+
+        Assert.Equal(2.0, sheet.Cells["A5"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountFunctionIncludingLogicalValues()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = true;
+        sheet.Cells["A3"].Value = false;
+        sheet.Cells["A4"].Value = 20;
+        sheet.Cells["A5"].Formula = "=COUNT(A1,A2,A3,A4)";
+
+        Assert.Equal(4.0, sheet.Cells["A5"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountFunctionIncludingTextRepresentationsOfNumbers()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "15";
+        sheet.Cells["A3"].Value = "text";
+        sheet.Cells["A4"].Value = "3.14";
+        sheet.Cells["A5"].Formula = "=COUNT(A1,A2,A3,A4)";
+
+        Assert.Equal(3.0, sheet.Cells["A5"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountFunctionIgnoringTextAndEmptyCells()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "text";
+        sheet.Cells["A3"].Value = "";
+        sheet.Cells["A4"].Value = 20;
+        sheet.Cells["A5"].Formula = "=COUNT(A1,A2,A3,A4)";
+
+        Assert.Equal(2.0, sheet.Cells["A5"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountFunctionIncludingZeroValues()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 0;
+        sheet.Cells["A3"].Value = 20;
+        sheet.Cells["A4"].Formula = "=COUNT(A1,A2,A3)";
+
+        Assert.Equal(3.0, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateCountFunctionWithAllNumericValues()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+        sheet.Cells["A4"].Formula = "=COUNT(A1,A2,A3)";
+
+        Assert.Equal(3.0, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldCreateRefErrorWhenCountRangeOutOfBounds()
+    {
+        sheet.Cells["A1"].Formula = "=COUNT(A2:A6)";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["A1"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/DayFunctionTests.cs

@@ -0,0 +1,32 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class DayFunctionTests
+{
+    [Fact]
+    public void Day_FromDateSerial_ReturnsDay()
+    {
+        var sheet = new Sheet(10, 10);
+        // Using DATEVALUE via VALUE on a date string to get a serial
+        sheet.Cells["A1"].Formula = "=DAY(VALUE(\"2011-04-15\"))";
+        Assert.Equal(15, sheet.Cells["A1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Day_FromDateValue_ReturnsDay()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2011, 4, 15));
+        sheet.Cells["B1"].Formula = "=DAY(A1)";
+        Assert.Equal(15, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Day_InvalidText_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=DAY(\"abc\")";
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/DeleteRowColumnTests.cs

@@ -0,0 +1,81 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class DeleteRowColumnTests
+{
+    [Fact]
+    public void DeleteColumn_ShiftsDataAndDecreasesColumnCount()
+    {
+        var sheet = new Sheet(3, 4);
+        sheet.Cells[0, 0].Value = "A";
+        sheet.Cells[0, 1].Value = "B";
+        sheet.Cells[0, 2].Value = "C";
+        sheet.Cells[0, 3].Value = "D";
+
+        sheet.DeleteColumn(1); // delete column B
+
+        Assert.Equal(3, sheet.ColumnCount);
+        Assert.Equal("A", sheet.Cells[0, 0].Value);
+        Assert.Equal("C", sheet.Cells[0, 1].Value);
+        Assert.Equal("D", sheet.Cells[0, 2].Value);
+    }
+
+    [Fact]
+    public void DeleteRow_ShiftsDataAndDecreasesRowCount()
+    {
+        var sheet = new Sheet(4, 2);
+        sheet.Cells[0, 0].Value = "R1";
+        sheet.Cells[1, 0].Value = "R2";
+        sheet.Cells[2, 0].Value = "R3";
+        sheet.Cells[3, 0].Value = "R4";
+
+        sheet.DeleteRow(1); // delete row 2
+
+        Assert.Equal(3, sheet.RowCount);
+        Assert.Equal("R1", sheet.Cells[0, 0].Value);
+        Assert.Equal("R3", sheet.Cells[1, 0].Value);
+        Assert.Equal("R4", sheet.Cells[2, 0].Value);
+    }
+
+    [Fact]
+    public void DeleteColumn_DoesNotAdjustFormulas_RefsBecomeError()
+    {
+        var sheet = new Sheet(5, 5);
+        sheet.Cells[0, 0].Value = 1;   // A1
+        sheet.Cells[0, 1].Value = 2;   // B1
+        sheet.Cells[0, 2].Value = 3;   // C1
+
+        // Formula in B2 references A1 and C1
+        sheet.Cells[1, 1].Formula = "=A1+C1";
+        Assert.Equal(4d, sheet.Cells[1, 1].Value);
+
+        // Delete referenced column A -> A1 becomes invalid => #REF!
+        sheet.DeleteColumn(0);
+
+        Assert.Equal(CellError.Ref, sheet.Cells[1, 0].Value);
+        Assert.Equal("=#REF!+C1", sheet.Cells[1, 0].Formula);
+    }
+
+    [Fact]
+    public void DeleteRow_DoesNotAdjustFormulas_RefsBecomeError()
+    {
+        var sheet = new Sheet(5, 5);
+        sheet.Cells[0, 0].Value = 1;   // A1
+        sheet.Cells[1, 0].Value = 2;   // A2
+        sheet.Cells[2, 0].Value = 3;   // A3
+
+        // Formula in B2 references A1 and A3
+        sheet.Cells[1, 1].Formula = "=A1+A3";
+        Assert.Equal(4d, sheet.Cells[1, 1].Value);
+
+        // Delete referenced row 1 -> A1 becomes invalid => #REF!
+        sheet.DeleteRow(0);
+
+        Assert.Equal(CellError.Ref, sheet.Cells[0, 1].Value);
+        Assert.Equal("=#REF!+A3", sheet.Cells[0, 1].Formula);
+    }
+
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/FilterCommandTests.cs

@@ -0,0 +1,146 @@
+using System;
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class FilterCommandTests
+{
+    private readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void Should_AddFilterWithCommand()
+    {
+        // Initially no filters
+        Assert.Empty(sheet.Filters);
+
+        // Create a filter
+        var filter = new SheetFilter(
+            new EqualToCriterion { Column = 0, Value = "Test" },
+            RangeRef.Parse("A1:A5")
+        );
+
+        // Execute the command
+        var command = new FilterCommand(sheet, filter);
+        var result = command.Execute();
+
+        // Command should succeed
+        Assert.True(result);
+
+        // Filter should be added
+        Assert.Single(sheet.Filters);
+        Assert.Contains(filter, sheet.Filters);
+    }
+
+    [Fact]
+    public void Should_UndoFilterCommand()
+    {
+        // Initially no filters
+        Assert.Empty(sheet.Filters);
+
+        // Create a filter
+        var filter = new SheetFilter(
+            new EqualToCriterion { Column = 0, Value = "Test" },
+            RangeRef.Parse("A1:A5")
+        );
+
+        // Execute the command
+        var command = new FilterCommand(sheet, filter);
+        command.Execute();
+
+        // Filter should be added
+        Assert.Single(sheet.Filters);
+
+        // Undo the command
+        command.Unexecute();
+
+        // Filter should be removed
+        Assert.Empty(sheet.Filters);
+    }
+
+    [Fact]
+    public void Should_WorkWithUndoRedoStack()
+    {
+        // Initially no filters
+        Assert.Empty(sheet.Filters);
+
+        // Create a filter
+        var filter = new SheetFilter(
+            new EqualToCriterion { Column = 0, Value = "Test" },
+            RangeRef.Parse("A1:A5")
+        );
+
+        // Execute the command through the undo/redo stack
+        var command = new FilterCommand(sheet, filter);
+        var result = sheet.Commands.Execute(command);
+
+        // Command should succeed
+        Assert.True(result);
+
+        // Filter should be added
+        Assert.Single(sheet.Filters);
+
+        // Undo should be available
+        Assert.True(sheet.Commands.CanUndo);
+
+        // Undo the command
+        sheet.Commands.Undo();
+
+        // Filter should be removed
+        Assert.Empty(sheet.Filters);
+
+        // Redo should be available
+        Assert.True(sheet.Commands.CanRedo);
+
+        // Redo the command
+        sheet.Commands.Redo();
+
+        // Filter should be added again
+        Assert.Single(sheet.Filters);
+    }
+
+    [Fact]
+    public void Should_HandleMultipleFilters()
+    {
+        // Initially no filters
+        Assert.Empty(sheet.Filters);
+
+        // Create multiple filters
+        var filter1 = new SheetFilter(
+            new EqualToCriterion { Column = 0, Value = "Test1" },
+            RangeRef.Parse("A1:A5")
+        );
+
+        var filter2 = new SheetFilter(
+            new EqualToCriterion { Column = 1, Value = "Test2" },
+            RangeRef.Parse("B1:B5")
+        );
+
+        // Execute commands through the undo/redo stack
+        var command1 = new FilterCommand(sheet, filter1);
+        var command2 = new FilterCommand(sheet, filter2);
+
+        sheet.Commands.Execute(command1);
+        sheet.Commands.Execute(command2);
+
+        // Both filters should be added
+        Assert.Equal(2, sheet.Filters.Count);
+        Assert.Contains(filter1, sheet.Filters);
+        Assert.Contains(filter2, sheet.Filters);
+
+        // Undo both commands
+        sheet.Commands.Undo(); // Undo filter2
+        sheet.Commands.Undo(); // Undo filter1
+
+        // No filters should remain
+        Assert.Empty(sheet.Filters);
+
+        // Redo both commands
+        sheet.Commands.Redo(); // Redo filter1
+        sheet.Commands.Redo(); // Redo filter2
+
+        // Both filters should be back
+        Assert.Equal(2, sheet.Filters.Count);
+        Assert.Contains(filter1, sheet.Filters);
+        Assert.Contains(filter2, sheet.Filters);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/FindFunctionTests.cs

@@ -0,0 +1,51 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class FindFunctionTests
+{
+    [Fact]
+    public void Find_CaseSensitive_MatchesUppercase()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "Miriam McGovern";
+        sheet.Cells["B1"].Formula = "=FIND(\"M\",A2)";
+        Assert.Equal(1d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Find_CaseSensitive_MatchesLowercase()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "Miriam McGovern";
+        sheet.Cells["B1"].Formula = "=FIND(\"m\",A2)";
+        Assert.Equal(6d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Find_WithStartNum()
+    {
+        var sheet = new Sheet(10, 30);
+        sheet.Cells["A1"].Value = "AYF0093.YoungMensApparel";
+        sheet.Cells["B1"].Formula = "=FIND(\"Y\",A1,8)";
+        Assert.Equal(9d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Find_EmptyFindText_ReturnsStart()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "abc";
+        sheet.Cells["B1"].Formula = "=FIND(\"\",A1,2)";
+        Assert.Equal(2d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Find_NotFound_ReturnsValue()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "abc";
+        sheet.Cells["B1"].Formula = "=FIND(\"z\",A1)";
+        Assert.Equal(CellError.Value, sheet.Cells["B1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/FormulaEvaluatorTests.cs

@@ -0,0 +1,298 @@
+using System;
+using System.Linq.Expressions;
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class FormulaEvaluationTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void ShouldEvaluateFormulaAfterSettingIt()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A2"].Formula = "=A1+1";
+
+        Assert.Equal(2d, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateFormulaAfterSettingValue()
+    {
+        sheet.Cells["A1"].Formula = "=A2+1";
+        sheet.Cells["A2"].Value = 1;
+
+        Assert.Equal(2d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldNotEvaluateFormulaIfEditing()
+    {
+        sheet.BeginUpdate();
+        sheet.Cells["A1"].Formula = "=A2+1";
+        sheet.Cells["A2"].Value = 1;
+
+        Assert.Null(sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateFormulaAfterEndingEdit()
+    {
+        sheet.BeginUpdate();
+        sheet.Cells["A1"].Formula = "=A2+1";
+        sheet.Cells["A2"].Value = 1;
+        sheet.EndUpdate();
+
+        Assert.Equal(2d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldSetCellValueToErrorValueIfStringIsUsedInBinaryOperation()
+    {
+        sheet.Cells["A1"].Formula = "=A2+1";
+        sheet.Cells["A2"].Value = "test";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldSetCellValueToErrorNameIfInvalidFunctionIsUsedInFormula()
+    {
+        sheet.Cells["A1"].Formula = "=INVALID_FUNCTION()";
+        sheet.Cells["A2"].Value = "test";
+
+        Assert.Equal(CellError.Name, sheet.Cells["A1"].Value);
+    }
+
+    [Theory]
+    [InlineData("=SUM(")]
+    [InlineData("=SUM(A2,")]
+    [InlineData("=SUM(A2:A2")]
+    public void ShouldSetCellValueToErrorNameIfIncompleteFunctionIsUsedInFormula(string formula)
+    {
+        sheet.Cells["A1"].Formula = formula;
+        sheet.Cells["A2"].Value = "test";
+
+        Assert.Equal(CellError.Name, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldSetCellValueToEqualsIfOnlyEqualsIsSetAsFormula()
+    {
+        sheet.Cells["A1"].SetValue("=");
+
+        Assert.Equal("=", sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateFormulaWhenDependencyIsChanged()
+    {
+        sheet.Cells["A1"].Formula = "=A2+1";
+        sheet.Cells["A2"].Formula = "=A3+1";
+        sheet.Cells["A3"].Value = 1;
+
+        Assert.Equal(3d, sheet.Cells["A1"].Value);
+        Assert.Equal(2d, sheet.Cells["A2"].Value);
+        Assert.Equal(1d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateFormulaWhenDependencyIsChangedAndEndEditIsCalled()
+    {
+        sheet.BeginUpdate();
+        sheet.Cells["A1"].Formula = "=A2+1";
+        sheet.Cells["A2"].Formula = "=A3+1";
+        sheet.Cells["A3"].Value = 1;
+        sheet.EndUpdate();
+
+        Assert.Equal(3d, sheet.Cells["A1"].Value);
+        Assert.Equal(2d, sheet.Cells["A2"].Value);
+        Assert.Equal(1d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldTreatEmptyValueAsZeroInFormula()
+    {
+        sheet.Cells["A1"].Formula = "=A2+1";
+
+        Assert.Equal(1d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldHandleSelfReferencingFormulas()
+    {
+        sheet.Cells["A1"].Formula = "=A1+1";
+
+        // Setting a value should not cause infinite recursion
+        sheet.Cells["A1"].Value = 1;
+
+        // The value should be stable and not cause infinite recursion
+        Assert.NotNull(sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldSetDiv0ErrorWhenDividingByZero()
+    {
+        sheet.Cells["A1"].Formula = "=A2/A3";
+        sheet.Cells["A2"].Value = 1;
+        sheet.Cells["A3"].Value = 0;
+
+        Assert.Equal(CellError.Div0, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldSetErrorToCircularWhenCellFormulasReferenceEachOther()
+    {
+        sheet.Cells["A1"].Formula = "=A2+1";
+        sheet.Cells["A2"].Formula = "=A1+1";
+
+        // The value should be an error
+        Assert.Equal(CellError.Circular, sheet.Cells["A1"].Value);
+        Assert.Equal(CellError.Circular, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnNameErrorForUnknownFunction()
+    {
+        sheet.Cells["A1"].Formula = "=UNKNOWN()";
+
+        Assert.Equal(CellError.Name, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldCreateRefErrorWhenOutOfBounds()
+    {
+        sheet.Cells["A1"].Formula = "=A6";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldCreateRefErrorWhenRangeOutOfBounds()
+    {
+        sheet.Cells["A1"].Formula = "=SUM(A2:A6)";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldCreateRefErrorWhenCountRangeOutOfBounds()
+    {
+        sheet.Cells["A1"].Formula = "=COUNT(A2:A6)";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldCreateRefErrorWhenCountaRangeOutOfBounds()
+    {
+        sheet.Cells["A1"].Formula = "=COUNTA(A2:A6)";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithDecimalValues()
+    {
+        sheet.Cells["A1"].Value = 0.5m;
+        sheet.Cells["A2"].Formula = "=IF(A1,\"True\",\"False\")";
+
+        Assert.Equal("True", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnNameErrorForUnknownFunctionUppercase()
+    {
+        sheet.Cells["A1"].Formula = "=UNKNOWNFUNCTION(1,2,3)";
+
+        Assert.Equal(CellError.Name, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnNameErrorForUnknownFunctionWithMixedCase()
+    {
+        sheet.Cells["A1"].Formula = "=UnknownFunction(1,2,3)";
+
+        Assert.Equal(CellError.Name, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnNameErrorForUnknownFunctionWithLowercase()
+    {
+        sheet.Cells["A1"].Formula = "=unknownfunction(1,2,3)";
+
+        Assert.Equal(CellError.Name, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateAndFunctionInIfStatementWithFalseCondition()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Value = 150;
+        sheet.Cells["A3"].Formula = "=IF(AND(A1>1,A2<100),A1,\"Out of range\")";
+
+        Assert.Equal("Out of range", sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithProvidedExample3()
+    {
+        sheet.Cells["A2"].Value = 75;
+        sheet.Cells["A3"].Formula = "=IF(OR(A2<0,A2>50),A2,\"The value is out of range\")";
+
+        Assert.Equal(75d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithOrFunction()
+    {
+        sheet.Cells["A1"].Value = false;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Formula = "=NOT(OR(A1,A2))";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    // IFERROR function tests are in IfErrorFunctionTests.cs
+
+    [Fact]
+    public void ShouldEvaluateSimpleDivisionByZero()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Formula = "=A1/0";
+
+        Assert.Equal(CellError.Div0, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void Evaluator_ShouldResolveCrossSheetCellReference()
+    {
+        var wb = new Workbook();
+        var s1 = wb.AddSheet("Sheet1", 5, 5);
+        var s2 = wb.AddSheet("Sheet2", 5, 5);
+
+        s2.Cells[0, 2].Value = 42; // C1 on Sheet2
+
+        s1.Cells[0, 0].Formula = "=Sheet2!C1"; // A1 on Sheet1 refers to Sheet2!C1
+
+        Assert.Equal(42d, s1.Cells[0, 0].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Evaluator_ShouldResolveCrossSheetRangeInFunction()
+    {
+        var wb = new Workbook();
+        var s1 = wb.AddSheet("Sheet1", 5, 5);
+        var s2 = wb.AddSheet("Sheet2", 5, 5);
+
+        s2.Cells[0, 0].Value = 1; // A1
+        s2.Cells[0, 1].Value = 2; // B1
+        s2.Cells[1, 0].Value = 3; // A2
+        s2.Cells[1, 1].Value = 4; // B2
+
+        s1.Cells[0, 0].Formula = "=SUM(Sheet2!A1:Sheet2!B2)";
+
+        Assert.Equal(10d, s1.Cells[0, 0].Data.GetValueOrDefault<double>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/FormulaLexerTests.cs

@@ -0,0 +1,143 @@
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+using System;
+using Xunit;
+
+public class FormulaLexerTests
+{
+    [Fact]
+    public void FormulaLexer_ShouldParseCellIdentifier()
+    {
+        var tokens = FormulaLexer.Scan("=A1");
+        Assert.Equal(FormulaTokenType.Equals, tokens[0].Type);
+        Assert.Equal(0, tokens[0].Start);
+        Assert.Equal(1, tokens[0].End);
+        Assert.Equal(FormulaTokenType.CellIdentifier, tokens[1].Type);
+        Assert.Equal("A1", tokens[1].Address.ToString());
+        Assert.Equal(1, tokens[1].Start);
+        Assert.Equal(3, tokens[1].End);
+    }
+
+    [Fact]
+    public void FormulaLexer_ShouldParseSimpleFormula()
+    {
+        var tokens = FormulaLexer.Scan("=A1+b2");
+        Assert.Equal(FormulaTokenType.Equals, tokens[0].Type);
+        Assert.Equal(0, tokens[0].Start);
+        Assert.Equal(1, tokens[0].End);
+        Assert.Equal(FormulaTokenType.CellIdentifier, tokens[1].Type);
+        Assert.Equal("A1", tokens[1].Value);
+        Assert.Equal(1, tokens[1].Start);
+        Assert.Equal(3, tokens[1].End);
+        Assert.Equal(FormulaTokenType.Plus, tokens[2].Type);
+        Assert.Equal(3, tokens[2].Start);
+        Assert.Equal(4, tokens[2].End);
+        Assert.Equal(FormulaTokenType.CellIdentifier, tokens[3].Type);
+        Assert.Equal("b2", tokens[3].Value);
+        Assert.Equal(4, tokens[3].Start);
+        Assert.Equal(6, tokens[3].End);
+    }
+
+    [Fact]
+    public void FormulaLexer_ShouldPreserveWhitespaceAsTrivia()
+    {
+        var tokens = FormulaLexer.Scan("= A1 + b2 ");
+
+        // Check that whitespace is preserved as trivia
+        Assert.Equal(FormulaTokenType.Equals, tokens[0].Type);
+        Assert.Empty(tokens[0].LeadingTrivia);
+        Assert.Single(tokens[0].TrailingTrivia);
+        Assert.Equal(FormulaTokenTriviaKind.Whitespace, tokens[0].TrailingTrivia[0].Kind);
+        Assert.Equal(" ", tokens[0].TrailingTrivia[0].Text);
+        Assert.Equal(0, tokens[0].Start);
+        Assert.Equal(2, tokens[0].End);
+
+        Assert.Equal(FormulaTokenType.CellIdentifier, tokens[1].Type);
+        Assert.Empty(tokens[1].LeadingTrivia);
+        Assert.Single(tokens[1].TrailingTrivia);
+        Assert.Equal(FormulaTokenTriviaKind.Whitespace, tokens[1].TrailingTrivia[0].Kind);
+        Assert.Equal(" ", tokens[1].TrailingTrivia[0].Text);
+        Assert.Equal(2, tokens[1].Start);
+        Assert.Equal(5, tokens[1].End);
+
+        Assert.Equal(FormulaTokenType.Plus, tokens[2].Type);
+        Assert.Empty(tokens[2].LeadingTrivia);
+        Assert.Single(tokens[2].TrailingTrivia);
+        Assert.Equal(FormulaTokenTriviaKind.Whitespace, tokens[2].TrailingTrivia[0].Kind);
+        Assert.Equal(" ", tokens[2].TrailingTrivia[0].Text);
+        Assert.Equal(5, tokens[2].Start);
+        Assert.Equal(7, tokens[2].End);
+
+        Assert.Equal(FormulaTokenType.CellIdentifier, tokens[3].Type);
+        Assert.Empty(tokens[3].LeadingTrivia);
+        Assert.Single(tokens[3].TrailingTrivia);
+        Assert.Equal(FormulaTokenTriviaKind.Whitespace, tokens[3].TrailingTrivia[0].Kind);
+        Assert.Equal(" ", tokens[3].TrailingTrivia[0].Text);
+        Assert.Equal(7, tokens[3].Start);
+        Assert.Equal(10, tokens[3].End);
+    }
+
+    [Fact]
+    public void FormulaLexer_ShouldPreserveMultipleWhitespaceAsTrivia()
+    {
+        var tokens = FormulaLexer.Scan("=  A1  +  b2  ");
+
+        // Check that multiple whitespace characters are preserved
+        Assert.Equal(FormulaTokenType.Equals, tokens[0].Type);
+        Assert.Single(tokens[0].TrailingTrivia);
+        Assert.Equal("  ", tokens[0].TrailingTrivia[0].Text);
+        Assert.Equal(0, tokens[0].Start);
+        Assert.Equal(3, tokens[0].End);
+
+        Assert.Equal(FormulaTokenType.CellIdentifier, tokens[1].Type);
+        Assert.Single(tokens[1].TrailingTrivia);
+        Assert.Equal("  ", tokens[1].TrailingTrivia[0].Text);
+        Assert.Equal(3, tokens[1].Start);
+        Assert.Equal(7, tokens[1].End);
+
+        Assert.Equal(FormulaTokenType.Plus, tokens[2].Type);
+        Assert.Single(tokens[2].TrailingTrivia);
+        Assert.Equal("  ", tokens[2].TrailingTrivia[0].Text);
+        Assert.Equal(7, tokens[2].Start);
+        Assert.Equal(10, tokens[2].End);
+
+        Assert.Equal(FormulaTokenType.CellIdentifier, tokens[3].Type);
+        Assert.Single(tokens[3].TrailingTrivia);
+        Assert.Equal("  ", tokens[3].TrailingTrivia[0].Text);
+        Assert.Equal(10, tokens[3].Start);
+        Assert.Equal(14, tokens[3].End);
+    }
+
+    [Fact]
+    public void FormulaLexer_ShouldPreserveLineEndingsAsTrivia()
+    {
+        var tokens = FormulaLexer.Scan("=A1\n+b2");
+
+        // Check that line endings are preserved as trivia
+        Assert.Equal(FormulaTokenType.Equals, tokens[0].Type);
+        Assert.Empty(tokens[0].LeadingTrivia);
+        Assert.Empty(tokens[0].TrailingTrivia);
+        Assert.Equal(0, tokens[0].Start);
+        Assert.Equal(1, tokens[0].End);
+
+        Assert.Equal(FormulaTokenType.CellIdentifier, tokens[1].Type);
+        Assert.Empty(tokens[1].LeadingTrivia);
+        Assert.Single(tokens[1].TrailingTrivia);
+        Assert.Equal(FormulaTokenTriviaKind.EndOfLine, tokens[1].TrailingTrivia[0].Kind);
+        Assert.Equal("\n", tokens[1].TrailingTrivia[0].Text);
+        Assert.Equal(1, tokens[1].Start);
+        Assert.Equal(4, tokens[1].End);
+
+        Assert.Equal(FormulaTokenType.Plus, tokens[2].Type);
+        Assert.Empty(tokens[2].LeadingTrivia);
+        Assert.Empty(tokens[2].TrailingTrivia);
+        Assert.Equal(4, tokens[2].Start);
+        Assert.Equal(5, tokens[2].End);
+
+        Assert.Equal(expected: FormulaTokenType.CellIdentifier, tokens[3].Type);
+        Assert.Empty(tokens[3].LeadingTrivia);
+        Assert.Empty(tokens[3].TrailingTrivia);
+        Assert.Equal(5, tokens[3].Start);
+        Assert.Equal(7, tokens[3].End);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/FormulaParserTests.cs

@@ -0,0 +1,644 @@
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+using System;
+using Xunit;
+
+public class FormulaParserTests
+{
+    [Fact]
+    public void FormulaParser_ShouldRequireEqualsAtStart()
+    {
+        var formula = "A1";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+        Assert.Contains("Unexpected token", syntaxTree.Errors[0]);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseNumberLiteral()
+    {
+        var formula = "=123";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        Assert.IsType<NumberLiteralSyntaxNode>(syntaxTree.Root);
+        var numberNode = (NumberLiteralSyntaxNode)syntaxTree.Root;
+        Assert.Equal(123, numberNode.Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseAdditionOfTwoNumberLiterals()
+    {
+        var formula = "=123+456";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        Assert.IsType<BinaryExpressionSyntaxNode>(syntaxTree.Root);
+        var binaryNode = (BinaryExpressionSyntaxNode)syntaxTree.Root;
+        Assert.Equal(BinaryOperator.Plus, binaryNode.Operator);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Left);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Right);
+        Assert.Equal(123, ((NumberLiteralSyntaxNode)binaryNode.Left).Token.IntValue);
+        Assert.Equal(456, ((NumberLiteralSyntaxNode)binaryNode.Right).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseAdditionOfMultipleNumberLiterals()
+    {
+        var formula = "=123+456+789";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<BinaryExpressionSyntaxNode>(node);
+        var binaryNode = (BinaryExpressionSyntaxNode)node;
+        Assert.Equal(BinaryOperator.Plus, binaryNode.Operator);
+        Assert.IsType<BinaryExpressionSyntaxNode>(binaryNode.Left);
+        var leftBinaryNode = (BinaryExpressionSyntaxNode)binaryNode.Left;
+        Assert.Equal(BinaryOperator.Plus, leftBinaryNode.Operator);
+        Assert.Equal(123, ((NumberLiteralSyntaxNode)leftBinaryNode.Left).Token.IntValue);
+        Assert.Equal(456, ((NumberLiteralSyntaxNode)leftBinaryNode.Right).Token.IntValue);
+        Assert.Equal(789, ((NumberLiteralSyntaxNode)binaryNode.Right).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseSubtractionOfTwoNumberLiterals()
+    {
+        var formula = "=123-456";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<BinaryExpressionSyntaxNode>(node);
+        var binaryNode = (BinaryExpressionSyntaxNode)node;
+        Assert.Equal(BinaryOperator.Minus, binaryNode.Operator);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Left);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Right);
+        Assert.Equal(123, ((NumberLiteralSyntaxNode)binaryNode.Left).Token.IntValue);
+        Assert.Equal(456, ((NumberLiteralSyntaxNode)binaryNode.Right).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseUnaryNegativeNumber()
+    {
+        var formula = "=-123";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        Assert.IsType<UnaryExpressionSyntaxNode>(syntaxTree.Root);
+        var unary = (UnaryExpressionSyntaxNode)syntaxTree.Root;
+        Assert.Equal(UnaryOperator.Negate, unary.Operator);
+        Assert.IsType<NumberLiteralSyntaxNode>(unary.Operand);
+        Assert.Equal(123, ((NumberLiteralSyntaxNode)unary.Operand).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseUnaryPlusNumber()
+    {
+        var formula = "=+123";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        Assert.IsType<UnaryExpressionSyntaxNode>(syntaxTree.Root);
+        var unary = (UnaryExpressionSyntaxNode)syntaxTree.Root;
+        Assert.Equal(UnaryOperator.Plus, unary.Operator);
+        Assert.IsType<NumberLiteralSyntaxNode>(unary.Operand);
+        Assert.Equal(123, ((NumberLiteralSyntaxNode)unary.Operand).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseUnaryPlusInFunctionArgument()
+    {
+        var formula = "=LEFT(A1,+1)";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        Assert.IsType<FunctionSyntaxNode>(syntaxTree.Root);
+        var fn = (FunctionSyntaxNode)syntaxTree.Root;
+        Assert.Equal("LEFT", fn.Name);
+        Assert.IsType<UnaryExpressionSyntaxNode>(fn.Arguments[1]);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseMultipleUnaryOperators()
+    {
+        var formula = "=-+-+3";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        // Expect nested unary nodes: - ( + ( - ( + 3 ) ) )
+        var node = syntaxTree.Root;
+        Assert.IsType<UnaryExpressionSyntaxNode>(node);
+        var u1 = (UnaryExpressionSyntaxNode)node; // '-'
+        Assert.Equal(UnaryOperator.Negate, u1.Operator);
+        Assert.IsType<UnaryExpressionSyntaxNode>(u1.Operand);
+        var u2 = (UnaryExpressionSyntaxNode)u1.Operand; // '+'
+        Assert.Equal(UnaryOperator.Plus, u2.Operator);
+        Assert.IsType<UnaryExpressionSyntaxNode>(u2.Operand);
+        var u3 = (UnaryExpressionSyntaxNode)u2.Operand; // '-'
+        Assert.Equal(UnaryOperator.Negate, u3.Operator);
+        Assert.IsType<UnaryExpressionSyntaxNode>(u3.Operand);
+        var u4 = (UnaryExpressionSyntaxNode)u3.Operand; // '+'
+        Assert.Equal(UnaryOperator.Plus, u4.Operator);
+        Assert.IsType<NumberLiteralSyntaxNode>(u4.Operand);
+        Assert.Equal(3, ((NumberLiteralSyntaxNode)u4.Operand).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseUnaryNegativeInFunctionArgument()
+    {
+        var formula = "=LEFT(A1,-1)";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        Assert.IsType<FunctionSyntaxNode>(syntaxTree.Root);
+        var fn = (FunctionSyntaxNode)syntaxTree.Root;
+        Assert.Equal("LEFT", fn.Name);
+        Assert.Equal(2, fn.Arguments.Count);
+        Assert.IsType<CellSyntaxNode>(fn.Arguments[0]);
+        Assert.IsType<UnaryExpressionSyntaxNode>(fn.Arguments[1]);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseSubtractionOfMultipleNumberLiterals()
+    {
+        var formula = "=123-456-789";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<BinaryExpressionSyntaxNode>(node);
+        var binaryNode = (BinaryExpressionSyntaxNode)node;
+        Assert.Equal(BinaryOperator.Minus, binaryNode.Operator);
+        Assert.IsType<BinaryExpressionSyntaxNode>(binaryNode.Left);
+        var leftBinaryNode = (BinaryExpressionSyntaxNode)binaryNode.Left;
+        Assert.Equal(BinaryOperator.Minus, leftBinaryNode.Operator);
+        Assert.Equal(123, ((NumberLiteralSyntaxNode)leftBinaryNode.Left).Token.IntValue);
+        Assert.Equal(456, ((NumberLiteralSyntaxNode)leftBinaryNode.Right).Token.IntValue);
+        Assert.Equal(789, ((NumberLiteralSyntaxNode)binaryNode.Right).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseMultiplicationOfTwoNumberLiterals()
+    {
+        var formula = "=123*456";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<BinaryExpressionSyntaxNode>(node);
+        var binaryNode = (BinaryExpressionSyntaxNode)node;
+        Assert.Equal(BinaryOperator.Multiply, binaryNode.Operator);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Left);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Right);
+        Assert.Equal(123, ((NumberLiteralSyntaxNode)binaryNode.Left).Token.IntValue);
+        Assert.Equal(456, ((NumberLiteralSyntaxNode)binaryNode.Right).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParse_MultiplicationPrecedence()
+    {
+        var formula = "=123+456*789";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<BinaryExpressionSyntaxNode>(node);
+        var binaryNode = (BinaryExpressionSyntaxNode)node;
+        Assert.Equal(BinaryOperator.Plus, binaryNode.Operator);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Left);
+        Assert.IsType<BinaryExpressionSyntaxNode>(binaryNode.Right);
+        var rightBinaryNode = (BinaryExpressionSyntaxNode)binaryNode.Right;
+        Assert.Equal(BinaryOperator.Multiply, rightBinaryNode.Operator);
+        Assert.Equal(456, ((NumberLiteralSyntaxNode)rightBinaryNode.Left).Token.IntValue);
+        Assert.Equal(789, ((NumberLiteralSyntaxNode)rightBinaryNode.Right).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseDivisionOfTwoNumberLiterals()
+    {
+        var formula = "=123/456";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<BinaryExpressionSyntaxNode>(node);
+        var binaryNode = (BinaryExpressionSyntaxNode)node;
+        Assert.Equal(BinaryOperator.Divide, binaryNode.Operator);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Left);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Right);
+        Assert.Equal(123, ((NumberLiteralSyntaxNode)binaryNode.Left).Token.IntValue);
+        Assert.Equal(456, ((NumberLiteralSyntaxNode)binaryNode.Right).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseParentheses()
+    {
+        var formula = "=(123+456)*789";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<BinaryExpressionSyntaxNode>(node);
+        var binaryNode = (BinaryExpressionSyntaxNode)node;
+        Assert.Equal(BinaryOperator.Multiply, binaryNode.Operator);
+        Assert.IsType<BinaryExpressionSyntaxNode>(binaryNode.Left);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Right);
+        var leftBinaryNode = (BinaryExpressionSyntaxNode)binaryNode.Left;
+        Assert.Equal(789, ((NumberLiteralSyntaxNode)binaryNode.Right).Token.IntValue);
+        Assert.Equal(BinaryOperator.Plus, leftBinaryNode.Operator);
+        Assert.Equal(123, ((NumberLiteralSyntaxNode)leftBinaryNode.Left).Token.IntValue);
+        Assert.Equal(456, ((NumberLiteralSyntaxNode)leftBinaryNode.Right).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseNestedParentheses()
+    {
+        var formula = "=((123+456)*789)/101112";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<BinaryExpressionSyntaxNode>(node);
+        var binaryNode = (BinaryExpressionSyntaxNode)node;
+        Assert.Equal(BinaryOperator.Divide, binaryNode.Operator);
+        Assert.IsType<BinaryExpressionSyntaxNode>(binaryNode.Left);
+        Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Right);
+        var leftBinaryNode = (BinaryExpressionSyntaxNode)binaryNode.Left;
+        Assert.Equal(101112, ((NumberLiteralSyntaxNode)binaryNode.Right).Token.IntValue);
+        Assert.Equal(BinaryOperator.Multiply, leftBinaryNode.Operator);
+        Assert.IsType<BinaryExpressionSyntaxNode>(leftBinaryNode.Left);
+        var leftLeftBinaryNode = (BinaryExpressionSyntaxNode)leftBinaryNode.Left;
+        Assert.Equal(123, ((NumberLiteralSyntaxNode)leftLeftBinaryNode.Left).Token.IntValue);
+        Assert.Equal(456, ((NumberLiteralSyntaxNode)leftLeftBinaryNode.Right).Token.IntValue);
+        Assert.Equal(789, ((NumberLiteralSyntaxNode)leftBinaryNode.Right).Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseCellIndentifer()
+    {
+        var formula = "=A1";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<CellSyntaxNode>(node);
+        var cellIdentifierNode = (CellSyntaxNode)node;
+        Assert.Equal("A1", cellIdentifierNode.Token.Address.ToString());
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseSheetQualifiedCellIdentifier()
+    {
+        var formula = "=Sheet2!C1";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<CellSyntaxNode>(node);
+        var cellIdentifierNode = (CellSyntaxNode)node;
+        Assert.Equal("C1", cellIdentifierNode.Token.Address.ToString());
+        Assert.Equal("Sheet2", cellIdentifierNode.Token.Address.Sheet);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseFunction()
+    {
+        var formula = "=SUM(A1,1)";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<FunctionSyntaxNode>(node);
+        var functionNode = (FunctionSyntaxNode)node;
+        Assert.Equal("SUM", functionNode.Name);
+        Assert.Equal(2, functionNode.Arguments.Count);
+        Assert.IsType<CellSyntaxNode>(functionNode.Arguments[0]);
+        Assert.IsType<NumberLiteralSyntaxNode>(functionNode.Arguments[1]);
+
+        var cellIdentifierNode = (CellSyntaxNode)functionNode.Arguments[0];
+        Assert.Equal("A1", cellIdentifierNode.Token.Address.ToString());
+        var numberLiteralNode = (NumberLiteralSyntaxNode)functionNode.Arguments[1];
+        Assert.Equal(1, numberLiteralNode.Token.IntValue);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseNestedFunctions()
+    {
+        var formula = "=SUM(A1,MAX(B1,C1))";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<FunctionSyntaxNode>(node);
+        var functionNode = (FunctionSyntaxNode)node;
+        Assert.Equal("SUM", functionNode.Name);
+        Assert.Equal(2, functionNode.Arguments.Count);
+        Assert.IsType<CellSyntaxNode>(functionNode.Arguments[0]);
+        Assert.IsType<FunctionSyntaxNode>(functionNode.Arguments[1]);
+
+        var cellIdentifierNode = (CellSyntaxNode)functionNode.Arguments[0];
+        Assert.Equal("A1", cellIdentifierNode.Token.Address.ToString());
+
+        var nestedFunctionNode = (FunctionSyntaxNode)functionNode.Arguments[1];
+        Assert.Equal("MAX", nestedFunctionNode.Name);
+        Assert.Equal(2, nestedFunctionNode.Arguments.Count);
+        Assert.IsType<CellSyntaxNode>(nestedFunctionNode.Arguments[0]);
+        Assert.IsType<CellSyntaxNode>(nestedFunctionNode.Arguments[1]);
+
+        var firstCellIdentifierNode = (CellSyntaxNode)nestedFunctionNode.Arguments[0];
+        var secondCellIdentifierNode = (CellSyntaxNode)nestedFunctionNode.Arguments[1];
+        Assert.Equal("B1", firstCellIdentifierNode.Token.Address.ToString());
+        Assert.Equal("C1", secondCellIdentifierNode.Token.Address.ToString());
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseFunctionWithNoArguments()
+    {
+        var formula = "=SUM()";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<FunctionSyntaxNode>(node);
+        var functionNode = (FunctionSyntaxNode)node;
+        Assert.Equal("SUM", functionNode.Name);
+        Assert.Empty(functionNode.Arguments);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseCellRange()
+    {
+        var formula = "=A1:A2";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<RangeSyntaxNode>(node);
+        var rangeNode = (RangeSyntaxNode)node;
+        Assert.Equal("A1", rangeNode.Start.Token.Address.ToString());
+        Assert.Equal("A2", rangeNode.End.Token.Address.ToString());
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseSheetQualifiedRange()
+    {
+        var formula = "=Sheet2!A1:Sheet2!B2";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<RangeSyntaxNode>(node);
+        var rangeNode = (RangeSyntaxNode)node;
+        Assert.Equal("A1", rangeNode.Start.Token.Address.ToString());
+        Assert.Equal("B2", rangeNode.End.Token.Address.ToString());
+        Assert.Equal("Sheet2", rangeNode.Start.Token.Address.Sheet);
+        Assert.Equal("Sheet2", rangeNode.End.Token.Address.Sheet);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseCellRangeInFunction()
+    {
+        var formula = "=SUM(A1:A2)";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<FunctionSyntaxNode>(node);
+        var functionNode = (FunctionSyntaxNode)node;
+        Assert.Equal("SUM", functionNode.Name);
+        Assert.Single(functionNode.Arguments);
+        Assert.IsType<RangeSyntaxNode>(functionNode.Arguments[0]);
+        var rangeNode = (RangeSyntaxNode)functionNode.Arguments[0];
+        Assert.Equal("A1", rangeNode.Start.Token.Address.ToString());
+        Assert.Equal("A2", rangeNode.End.Token.Address.ToString());
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldHandleInvalidRange()
+    {
+        var formula = "=A2:A1";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<RangeSyntaxNode>(node);
+        var rangeNode = (RangeSyntaxNode)node;
+        Assert.Equal("A2", rangeNode.Start.Token.Address.ToString());
+        Assert.Equal("A1", rangeNode.End.Token.Address.ToString());
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldHandleSingleCellRange()
+    {
+        var formula = "=A1:A1";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<RangeSyntaxNode>(node);
+        var rangeNode = (RangeSyntaxNode)node;
+        Assert.Equal("A1", rangeNode.Start.Token.Address.ToString());
+        Assert.Equal("A1", rangeNode.End.Token.Address.ToString());
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldHandleMultiColumnRange()
+    {
+        var formula = "=A1:B1";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<RangeSyntaxNode>(node);
+        var rangeNode = (RangeSyntaxNode)node;
+        Assert.Equal("A1", rangeNode.Start.Token.Address.ToString());
+        Assert.Equal("B1", rangeNode.End.Token.Address.ToString());
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldHandleMultiRowRange()
+    {
+        var formula = "=A1:A2";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<RangeSyntaxNode>(node);
+        var rangeNode = (RangeSyntaxNode)node;
+        Assert.Equal("A1", rangeNode.Start.Token.Address.ToString());
+        Assert.Equal("A2", rangeNode.End.Token.Address.ToString());
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldHandleMultiCellRange()
+    {
+        var formula = "=A1:B2";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.IsType<RangeSyntaxNode>(node);
+        var rangeNode = (RangeSyntaxNode)node;
+        Assert.Equal("A1", rangeNode.Start.Token.Address.ToString());
+        Assert.Equal("B2", rangeNode.End.Token.Address.ToString());
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldAddErrorOnInvalidFormula()
+    {
+        var formula = "A1"; // Missing equals sign
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+        Assert.Contains("Unexpected token", syntaxTree.Errors[0]);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldReturnPartialExpressionOnIncompleteExpression()
+    {
+        var formula = "=123+"; // Incomplete expression
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+        Assert.IsType<BinaryExpressionSyntaxNode>(syntaxTree.Root);
+        if (syntaxTree.Root is BinaryExpressionSyntaxNode binaryNode)
+        {
+            Assert.Equal(BinaryOperator.Plus, binaryNode.Operator);
+            Assert.IsType<NumberLiteralSyntaxNode>(binaryNode.Left);
+            Assert.Equal(123, ((NumberLiteralSyntaxNode)binaryNode.Left).Token.IntValue);
+        }
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldAddErrorOnIncompleteExpression()
+    {
+        var formula = "=123+"; // Incomplete expression
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldReturnPartialFunctionOnMissingCloseParen()
+    {
+        var formula = "=SUM(A1"; // Missing closing parenthesis
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+        Assert.IsType<FunctionSyntaxNode>(syntaxTree.Root);
+        var functionNode = (FunctionSyntaxNode)syntaxTree.Root;
+        Assert.Equal("SUM", functionNode.Name);
+        Assert.Single(functionNode.Arguments);
+        Assert.IsType<CellSyntaxNode>(functionNode.Arguments[0]);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldAddErrorOnInvalidFunctionSyntax()
+    {
+        var formula = "=SUM(A1"; // Missing closing parenthesis
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseGroupedExpression()
+    {
+        var formula = "=(A1)"; // Parentheses without function name should parse as grouped expression
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors); // This should actually succeed as it's a valid grouped expression
+        Assert.IsType<CellSyntaxNode>(syntaxTree.Root);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldReturnPartialRangeOnIncompleteRange()
+    {
+        var formula = "=A1:"; // Incomplete range
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+        Assert.NotNull(syntaxTree.Root);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldAddErrorOnInvalidRange()
+    {
+        var formula = "=A1:"; // Incomplete range
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldHandleUnterminatedString()
+    {
+        var formula = "=\"hello"; // Unterminated string literal
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors); // Should succeed as lexer handles unterminated strings
+        Assert.IsType<StringLiteralSyntaxNode>(syntaxTree.Root);
+        var stringNode = (StringLiteralSyntaxNode)syntaxTree.Root;
+        Assert.Equal("hello", stringNode.Token.Value);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldHandleMissingOperand()
+    {
+        var formula = "=*5"; // Missing left operand
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors); // Should have errors
+        Assert.NotNull(syntaxTree.Root);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldReturnPartialExpressionOnUnbalancedParentheses()
+    {
+        var formula = "=(A1+B1"; // Missing closing parenthesis
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+        Assert.IsType<BinaryExpressionSyntaxNode>(syntaxTree.Root); // Should return the binary expression inside
+        var binaryNode = (BinaryExpressionSyntaxNode)syntaxTree.Root;
+        Assert.Equal(BinaryOperator.Plus, binaryNode.Operator);
+        Assert.IsType<CellSyntaxNode>(binaryNode.Left);
+        Assert.IsType<CellSyntaxNode>(binaryNode.Right);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldAddErrorOnUnbalancedParentheses()
+    {
+        var formula = "=(A1+B1"; // Missing closing parenthesis
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldReturnPartialFunctionOnIncompleteArguments()
+    {
+        var formula = "=SUM(A1,"; // Incomplete function arguments
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+        Assert.IsType<FunctionSyntaxNode>(syntaxTree.Root);
+        var functionNode = (FunctionSyntaxNode)syntaxTree.Root;
+        Assert.Equal("SUM", functionNode.Name);
+        Assert.True(functionNode.Arguments.Count >= 1); // Should have at least the first argument
+        Assert.IsType<CellSyntaxNode>(functionNode.Arguments[0]);
+    }
+
+    [Fact]
+    public void FormulaParser_DefaultBehavior_ShouldStillWork()
+    {
+        // Test that default behavior still works as before
+        var formula = "=123+456";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var node = syntaxTree.Root;
+        Assert.NotNull(node);
+        Assert.IsType<BinaryExpressionSyntaxNode>(node);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseBooleanTrue()
+    {
+        var formula = "=TRUE";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        Assert.IsType<BooleanLiteralSyntaxNode>(syntaxTree.Root);
+        var boolNode = (BooleanLiteralSyntaxNode)syntaxTree.Root;
+        Assert.Equal("TRUE", boolNode.Token.Value);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseBooleanFalse_Lowercase()
+    {
+        var formula = "=false";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        Assert.IsType<BooleanLiteralSyntaxNode>(syntaxTree.Root);
+        var boolNode = (BooleanLiteralSyntaxNode)syntaxTree.Root;
+        Assert.Equal("false", boolNode.Token.Value);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParseBooleanInFunction()
+    {
+        var formula = "=TEXTJOIN(\", \", TRUE, A1:A2)";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.Empty(syntaxTree.Errors);
+        var fn = Assert.IsType<FunctionSyntaxNode>(syntaxTree.Root);
+        Assert.Equal("TEXTJOIN", fn.Name);
+        Assert.IsType<BooleanLiteralSyntaxNode>(fn.Arguments[1]);
+    }
+
+    [Fact]
+    public void FormulaParser_ShouldParse_Percent()
+    {
+        var formula = "=$%";
+        var syntaxTree = FormulaParser.Parse(formula);
+        Assert.NotEmpty(syntaxTree.Errors);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/FunctionRegistryTests.cs

@@ -0,0 +1,74 @@
+using System;
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class FunctionRegistryTests
+{
+    private readonly FunctionStore functionRegistry = new();
+
+    [Theory]
+    [InlineData(2, -1)]
+    [InlineData(4, -1)]
+    [InlineData(5, 0)]
+    [InlineData(6, 0)]
+    [InlineData(7, 1)]
+    [InlineData(8, 1)]
+    [InlineData(9, 2)]
+    [InlineData(10, 2)]
+    public void Basic_Function_Provides_Correct_Arg_Index(int cursorPosition, int expectedArgIndex)
+    {
+        var func = "=SUM(1,2,3)";
+        var result = functionRegistry.CreateFunctionHint(func, cursorPosition);
+
+        Assert.NotNull(result);
+
+        Assert.Equal(expectedArgIndex, result.ArgumentIndex);
+        Assert.IsType<SumFunction>(result.Function);
+    }
+    [Theory]
+    [InlineData(5, 0, "=SUM(")]
+    [InlineData(4, -1, "=SUM(")]
+    public void Basic_Function_Provides_Correct_Arg_Index_With_IncompleteFormula(int cursorPosition, int expectedArgIndex, string formula)
+    {
+        var result = functionRegistry.CreateFunctionHint(formula, cursorPosition);
+
+        Assert.NotNull(result);
+
+        Assert.Equal(expectedArgIndex, result.ArgumentIndex);
+        Assert.IsType<SumFunction>(result.Function);
+    }
+
+    [Fact]
+    public void Position_Outside_Of_Formula_Returns_null()
+    {
+        var func = "=1 + SUM(1,2, 3) + 2";
+        var result = functionRegistry.CreateFunctionHint(func, 0);
+
+        Assert.Null(result);
+
+        result = functionRegistry.CreateFunctionHint(func, 5);
+        Assert.Null(result);
+
+        result = functionRegistry.CreateFunctionHint(func, 16);
+        Assert.Null(result);
+    }
+
+    [Theory]
+    [InlineData(5, 0, typeof(SumFunction))]
+    [InlineData(7, 1, typeof(SumFunction))]
+    [InlineData(8, -1, typeof(CountFunction))]
+    [InlineData(13, 0, typeof(CountFunction))]
+    [InlineData(15, 1, typeof(CountFunction))]
+    [InlineData(17, 1, typeof(SumFunction))]
+    public void Nested_Function_Produces_Correct_ArgIndex(int cursorPosition, int expectedArgIndex, Type expectedFunction)
+    {
+        var func = "=SUM(1,COUNT(1,2),3)";
+        var result = functionRegistry.CreateFunctionHint(func, cursorPosition);
+
+        Assert.NotNull(result);
+
+        Assert.Equal(expectedArgIndex, result.ArgumentIndex);
+        Assert.IsType(expectedFunction, result.Function);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/HorizontalLookupFunctionTests.cs

@@ -0,0 +1,59 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class HorizontalLookupFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldFindExactMatchInTwoRowRange()
+    {
+        sheet.Cells["A1"].Value = "Size";
+        sheet.Cells["B1"].Value = "Color";
+        sheet.Cells["A2"].Value = "M";
+        sheet.Cells["B2"].Value = "Blue";
+
+        sheet.Cells["C1"].Formula = "=HLOOKUP(\"Color\",A1:B2,2,0)";
+
+        Assert.Equal("Blue", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnNAWhenNoExactMatch()
+    {
+        sheet.Cells["A1"].Value = "Size";
+        sheet.Cells["A2"].Value = "M";
+
+        sheet.Cells["B1"].Formula = "=HLOOKUP(\"Color\",A1:A2,2,0)";
+
+        Assert.Equal(CellError.NA, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldFindApproximateMatchInSortedTopRow()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["B1"].Value = 20;
+        sheet.Cells["C1"].Value = 30;
+
+        sheet.Cells["A2"].Value = "Low";
+        sheet.Cells["B2"].Value = "Medium";
+        sheet.Cells["C2"].Value = "High";
+
+        sheet.Cells["D1"].Formula = "=HLOOKUP(25,A1:C2,2,1)";
+
+        Assert.Equal("Medium", sheet.Cells["D1"].Value);
+    }
+
+    [Fact]
+    public void ShouldErrorWhenIndexOutOfRange()
+    {
+        sheet.Cells["A1"].Value = "X";
+        sheet.Cells["A2"].Value = 1;
+
+        sheet.Cells["B1"].Formula = "=HLOOKUP(\"X\",A1:A2,3,0)";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["B1"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/HourFunctionTests.cs

@@ -0,0 +1,33 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class HourFunctionTests
+{
+    [Fact]
+    public void Hour_FromFraction_Returns18()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Data = CellData.FromNumber(0.75); // 18:00
+        sheet.Cells["B2"].Formula = "=HOUR(A2)";
+        Assert.Equal(18, sheet.Cells["B2"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Hour_FromDateTimeValue_ReturnsHour()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A3"].Data = CellData.FromDate(new System.DateTime(2011, 7, 18, 7, 45, 0));
+        sheet.Cells["B3"].Formula = "=HOUR(A3)";
+        Assert.Equal(7, sheet.Cells["B3"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Hour_FromDateOnly_ReturnsZero()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A4"].Data = CellData.FromDate(new System.DateTime(2012, 4, 21));
+        sheet.Cells["B4"].Formula = "=HOUR(A4)";
+        Assert.Equal(0, sheet.Cells["B4"].Data.GetValueOrDefault<double>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/IfErrorFunctionTests.cs

@@ -0,0 +1,138 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class IfErrorFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithNoError()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 2;
+        sheet.Cells["A3"].Formula = "=IFERROR(A1/A2, \"Error in calculation\")";
+
+        Assert.Equal(5d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithDivisionByZero()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 0;
+        sheet.Cells["A3"].Formula = "=IFERROR(A1/A2, \"Error in calculation\")";
+
+        Assert.Equal("Error in calculation", sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithReferenceError()
+    {
+        sheet.Cells["A1"].Formula = "=IFERROR(A6, \"Error in calculation\")";
+
+        Assert.Equal("Error in calculation", sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithEmptyStringForError()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 0;
+        sheet.Cells["A3"].Formula = "=IFERROR(A1/A2, \"\")";
+
+        Assert.Equal("", sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithNumericErrorValue()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 0;
+        sheet.Cells["A3"].Formula = "=IFERROR(A1/A2, 0)";
+
+        Assert.Equal(0d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithEmptyCellAsErrorValue()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 0;
+        sheet.Cells["A3"].Formula = "=IFERROR(A1/A2, A4)";
+
+        Assert.Equal("", sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithEmptyCellAsValue()
+    {
+        sheet.Cells["A1"].Formula = "=IFERROR(A2, \"Empty cell\")";
+
+        Assert.Equal("", sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithStringValue()
+    {
+        sheet.Cells["A1"].Value = "Hello";
+        sheet.Cells["A2"].Formula = "=IFERROR(A1, \"Error\")";
+
+        Assert.Equal("Hello", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithBooleanValue()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Formula = "=IFERROR(A1, \"Error\")";
+
+        Assert.Equal(true, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForIfErrorTooFewArguments()
+    {
+        sheet.Cells["A1"].Formula = "=IFERROR(A2)";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForIfErrorTooManyArguments()
+    {
+        sheet.Cells["A1"].Formula = "=IFERROR(A2, \"Error\", \"Extra\")";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithNestedFormula()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 0;
+        sheet.Cells["A3"].Formula = "=IFERROR(A1/A2, IFERROR(A1/0, \"Nested Error\"))";
+
+        Assert.Equal("Nested Error", sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithSumFunction()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Formula = "=IFERROR(SUM(A1:A2), \"Error\")";
+
+        Assert.Equal(30d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfErrorFunctionWithSumFunctionError()
+    {
+        sheet.Cells["A1"].Formula = "=IFERROR(SUM(A6:A8), \"Error\")";
+
+        Assert.Equal("Error", sheet.Cells["A1"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/IfFunctionTests.cs

@@ -0,0 +1,178 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class IfFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithTrueCondition()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A2"].Formula = "=IF(A1=1,\"Yes\",\"No\")";
+
+        Assert.Equal("Yes", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithFalseCondition()
+    {
+        sheet.Cells["A1"].Value = 2;
+        sheet.Cells["A2"].Formula = "=IF(A1=1,\"Yes\",\"No\")";
+
+        Assert.Equal("No", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithNumericComparison()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 5;
+        sheet.Cells["A3"].Formula = "=IF(A1>A2,\"Over Budget\",\"Within Budget\")";
+
+        Assert.Equal("Over Budget", sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithNumericResult()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 5;
+        sheet.Cells["A3"].Formula = "=IF(A1>A2,A1-A2,0)";
+
+        Assert.Equal(5d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithTwoArguments()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A2"].Formula = "=IF(A1=1,\"True\")";
+
+        Assert.Equal("True", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithTwoArgumentsFalseCondition()
+    {
+        sheet.Cells["A1"].Value = 0;
+        sheet.Cells["A2"].Formula = "=IF(A1=1,\"True\")";
+
+        Assert.Equal(false, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithZeroAsFalse()
+    {
+        sheet.Cells["A1"].Value = 0;
+        sheet.Cells["A2"].Formula = "=IF(A1,\"True\",\"False\")";
+
+        Assert.Equal("False", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithNonZeroAsTrue()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Formula = "=IF(A1,\"True\",\"False\")";
+
+        Assert.Equal("True", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateToErrorIfFunctionWithStringCondition()
+    {
+        sheet.Cells["A1"].Value = "test";
+        sheet.Cells["A2"].Formula = "=IF(A1,\"Not Empty\",\"Empty\")";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithEmptyStringCondition()
+    {
+        sheet.Cells["A2"].Formula = "=IF(A1,\"Not Empty\",\"Empty\")";
+
+        Assert.Equal("Empty", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithNullCondition()
+    {
+        sheet.Cells["A2"].Formula = "=IF(A1,\"Not Empty\",\"Empty\")";
+
+        Assert.Equal("Empty", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForTooFewArguments()
+    {
+        sheet.Cells["A1"].Formula = "=IF(A2)";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForTooManyArguments()
+    {
+        sheet.Cells["A1"].Formula = "=IF(A2,\"True\",\"False\",\"Extra\")";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldPropagateErrorFromCondition()
+    {
+        sheet.Cells["A1"].Formula = "=IF(A6,\"True\",\"False\")";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldPropagateErrorFromTrueValue()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A2"].Formula = "=IF(A1=1,A6,\"False\")";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldPropagateErrorFromFalseValue()
+    {
+        sheet.Cells["A1"].Value = 0;
+        sheet.Cells["A2"].Formula = "=IF(A1=1,\"True\",A6)";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNestedIfFunction()
+    {
+        sheet.Cells["A1"].Value = 85;
+        sheet.Cells["A2"].Formula = "=IF(A1>=90,\"A\",IF(A1>=80,\"B\",IF(A1>=70,\"C\",\"F\")))";
+
+        Assert.Equal("B", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithBooleanValues()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Formula = "=IF(A1,\"True\",\"False\")";
+
+        Assert.Equal("True", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateIfFunctionWithDecimalValues()
+    {
+        sheet.Cells["A1"].Value = 0.5m;
+        sheet.Cells["A2"].Formula = "=IF(A1,\"True\",\"False\")";
+
+        Assert.Equal("True", sheet.Cells["A2"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/IndexFunctionTests.cs

@@ -0,0 +1,100 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class IndexFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    void Seed()
+    {
+        sheet.Cells["A2"].Value = "Apples";
+        sheet.Cells["B2"].Value = "Lemons";
+        sheet.Cells["A3"].Value = "Bananas";
+        sheet.Cells["B3"].Value = "Pears";
+    }
+
+    [Fact]
+    public void ShouldReturnIntersectionValue()
+    {
+        Seed();
+
+        sheet.Cells["C1"].Formula = "=INDEX(A2:B3,2,2)";
+        Assert.Equal("Pears", sheet.Cells["C1"].Value);
+
+        sheet.Cells["C2"].Formula = "=INDEX(A2:B3,2,1)";
+        Assert.Equal("Bananas", sheet.Cells["C2"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnRefErrorIfOutOfRange()
+    {
+        // numeric values just to ensure range exists
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["B1"].Value = 2;
+        sheet.Cells["A2"].Value = 3;
+        sheet.Cells["B2"].Value = 4;
+
+        sheet.Cells["C1"].Formula = "=INDEX(A1:B2,3,1)"; // row 3 out of 2 rows
+        Assert.Equal(CellError.Ref, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldDefaultColumnToFirstWhenOmitted()
+    {
+        Seed();
+        sheet.Cells["C1"].Formula = "=INDEX(A2:B3,2)"; // column omitted -> first column
+        Assert.Equal("Bananas", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldUseAreaOneWhenSpecified()
+    {
+        Seed();
+        sheet.Cells["C1"].Formula = "=INDEX(A2:B3,2,2,1)";
+        Assert.Equal("Pears", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorWhenAreaGreaterThanOne()
+    {
+        Seed();
+        sheet.Cells["C1"].Formula = "=INDEX(A2:B3,1,1,2)";
+        Assert.Equal(CellError.Value, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnFirstOfEntireColumnWhenRowIsZero()
+    {
+        Seed();
+        sheet.Cells["C1"].Formula = "=INDEX(A2:B3,0,2)";
+        Assert.Equal("Lemons", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnFirstOfEntireRowWhenColumnIsZero()
+    {
+        Seed();
+        sheet.Cells["C1"].Formula = "=INDEX(A2:B3,2,0)";
+        Assert.Equal("Bananas", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorWhenBothRowAndColumnOmitted()
+    {
+        Seed();
+        sheet.Cells["C1"].Formula = "=INDEX(A2:B3)";
+        Assert.Equal(CellError.Value, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnRefErrorOnNegativeIndices()
+    {
+        Seed();
+        sheet.Cells["C1"].Formula = "=INDEX(A2:B3,0-1,1)"; // -1
+        Assert.Equal(CellError.Ref, sheet.Cells["C1"].Value);
+
+        sheet.Cells["C2"].Formula = "=INDEX(A2:B3,1,0-1)"; // -1
+        Assert.Equal(CellError.Ref, sheet.Cells["C2"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/InsertRowColumnTests.cs

@@ -0,0 +1,64 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class InsertRowColumnTests
+{
+    [Fact]
+    public void InsertColumn_ShiftsReferencesAndValues()
+    {
+        var sheet = new Sheet(5, 5);
+
+        sheet.Cells[1, 0].Value = 1;   // A2
+        sheet.Cells[1, 1].Formula = "=A2+10"; // B2
+        Assert.Equal(11d, sheet.Cells[1, 1].Value);
+
+        // Insert a column before A (index 0)
+        sheet.InsertColumn(0, 1);
+
+        // Values shift right
+        Assert.Equal(1d, sheet.Cells[1, 1].Value); // A2 moved to B2
+
+        // Formula shifts position and updates referenced address
+        Assert.Equal("=B2+10", sheet.Cells[1, 2].Formula); // original B2 moved to C2
+        Assert.Equal(11d, sheet.Cells[1, 2].Value);
+    }
+
+    [Fact]
+    public void InsertRow_ShiftsReferencesAndValues()
+    {
+        var sheet = new Sheet(5, 5);
+
+        sheet.Cells[1, 0].Value = 1;   // A2
+        sheet.Cells[1, 1].Formula = "=A2+10"; // B2
+        Assert.Equal(11d, sheet.Cells[1, 1].Value);
+
+        // Insert a row before row 2 (index 1)
+        sheet.InsertRow(1, 1);
+
+        // Values shift down
+        Assert.Equal(1d, sheet.Cells[2, 0].Value); // A2 moved to A3
+
+        // Formula shifts position and updates referenced address
+        Assert.Equal("=A3+10", sheet.Cells[2, 1].Formula); // original B2 moved to B3
+        Assert.Equal(11d, sheet.Cells[2, 1].Value);
+    }
+
+    [Fact]
+    public void InsertRow_IncreasesRowCount()
+    {
+        var sheet = new Sheet(5, 5);
+        sheet.InsertRow(2, 2);
+        Assert.Equal(7, sheet.RowCount);
+    }
+
+    [Fact]
+    public void InsertColumn_IncreasesColumnCount()
+    {
+        var sheet = new Sheet(5, 5);
+        sheet.InsertColumn(3, 3);
+        Assert.Equal(8, sheet.ColumnCount);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/IntFunctionTests.cs

@@ -0,0 +1,30 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class IntFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldRoundDownPositive()
+    {
+        sheet.Cells["A1"].Formula = "=INT(8.9)";
+        Assert.Equal(8d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldRoundDownNegative()
+    {
+        sheet.Cells["A1"].Formula = "=INT(0-8.9)";
+        Assert.Equal(-9d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnDecimalPart()
+    {
+        sheet.Cells["A2"].Value = 19.5;
+        sheet.Cells["A1"].Formula = "=A2-INT(A2)";
+        Assert.Equal(0.5, sheet.Cells["A1"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/LargeFunctionTests.cs

@@ -0,0 +1,74 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class LargeFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldReturnKthLargestAcrossRange()
+    {
+        // Populate A2:B6 as in example
+        sheet.Cells["A2"].Value = 3;
+        sheet.Cells["A3"].Value = 4;
+        sheet.Cells["A4"].Value = 5;
+        sheet.Cells["A5"].Value = 2;
+        sheet.Cells["A6"].Value = 3;
+
+        sheet.Cells["B2"].Value = 4;
+        sheet.Cells["B3"].Value = 5;
+        sheet.Cells["B4"].Value = 6;
+        sheet.Cells["B5"].Value = 4;
+        sheet.Cells["B6"].Value = 7;
+
+        sheet.Cells["C1"].Formula = "=LARGE(A2:B6,3)";
+
+        Assert.Equal(5d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturn7thLargestAsFour()
+    {
+        sheet.Cells["A2"].Value = 3;
+        sheet.Cells["A3"].Value = 4;
+        sheet.Cells["A4"].Value = 5;
+        sheet.Cells["A5"].Value = 2;
+        sheet.Cells["A6"].Value = 3;
+
+        sheet.Cells["B2"].Value = 4;
+        sheet.Cells["B3"].Value = 5;
+        sheet.Cells["B4"].Value = 6;
+        sheet.Cells["B5"].Value = 4;
+        sheet.Cells["B6"].Value = 7;
+
+        sheet.Cells["C1"].Formula = "=LARGE(A2:B6,7)";
+
+        Assert.Equal(4d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnNumErrorForInvalidK()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A2"].Value = 2;
+        sheet.Cells["A3"].Value = 3;
+
+        sheet.Cells["B1"].Formula = "=LARGE(A1:A3,0)";
+        Assert.Equal(CellError.Num, sheet.Cells["B1"].Value);
+
+        sheet.Cells["B2"].Formula = "=LARGE(A1:A3,5)";
+        Assert.Equal(CellError.Num, sheet.Cells["B2"].Value);
+    }
+
+    [Fact]
+    public void ShouldIgnoreNonNumericCellsInArray()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "x"; // ignored
+        sheet.Cells["A3"].Value = 7;
+
+        sheet.Cells["B1"].Formula = "=LARGE(A1:A3,2)";
+        Assert.Equal(7d, sheet.Cells["B1"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/LeftFunctionTests.cs

@@ -0,0 +1,42 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class LeftFunctionTests
+{
+    [Fact]
+    public void Left_WithCount_ReturnsPrefix()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "Sale Price";
+        sheet.Cells["B1"].Formula = "=LEFT(A2,4)";
+        Assert.Equal("Sale", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Left_OmittedCount_DefaultsToOne()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A3"].Value = "Sweden";
+        sheet.Cells["B1"].Formula = "=LEFT(A3)";
+        Assert.Equal("S", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Left_CountExceedsLength_ReturnsWhole()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "Hi";
+        sheet.Cells["B1"].Formula = "=LEFT(A1,5)";
+        Assert.Equal("Hi", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Left_NegativeCount_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "Test";
+        sheet.Cells["B1"].Formula = "=LEFT(A1,-1)";
+        Assert.Equal(CellError.Value, sheet.Cells["B1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/LenFunctionTests.cs

@@ -0,0 +1,59 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class LenFunctionTests
+{
+    [Fact]
+    public void Len_String_ReturnsLength()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "Phoenix, AZ"; // 11 characters
+        sheet.Cells["B1"].Formula = "=LEN(A1)";
+        Assert.Equal(11d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Len_BooleanCellTrue_ReturnsFour()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["B1"].Formula = "=LEN(A1)";
+        Assert.Equal(4d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Len_BooleanCellFalse_ReturnsFive()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = false;
+        sheet.Cells["B1"].Formula = "=LEN(A1)";
+        Assert.Equal(5d, sheet.Cells["B1"].Data.Value);
+    }
+    [Fact]
+    public void Len_Empty_ReturnsZero()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = null; // empty
+        sheet.Cells["B1"].Formula = "=LEN(A1)";
+        Assert.Equal(0d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Len_String_WithSpaces_CountsSpaces()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "     One   "; // 11 characters including spaces
+        sheet.Cells["B1"].Formula = "=LEN(A1)";
+        Assert.Equal(11d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Len_Number_TreatsAsTextLength()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = 123.45; // "123.45" length 6
+        sheet.Cells["B1"].Formula = "=LEN(A1)";
+        Assert.Equal(6d, sheet.Cells["B1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/LowerFunctionTests.cs

@@ -0,0 +1,24 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class LowerFunctionTests
+{
+    [Fact]
+    public void Lower_ConvertsToLowercase()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "E. E. Cummings";
+        sheet.Cells["B1"].Formula = "=LOWER(A2)";
+        Assert.Equal("e. e. cummings", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Lower_IgnoresNonLetters()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A3"].Value = "Apt. 2B";
+        sheet.Cells["B1"].Formula = "=LOWER(A3)";
+        Assert.Equal("apt. 2b", sheet.Cells["B1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/MaxAllFunctionTests.cs

@@ -0,0 +1,64 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class MaxAllFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldEvaluateLogicalValuesInRange()
+    {
+        sheet.Cells["A1"].Value = true;   // 1
+        sheet.Cells["A2"].Value = false;  // 0
+        sheet.Cells["A3"].Value = 5;      // 5
+
+        sheet.Cells["B1"].Formula = "=MAXA(A1:A3)";
+
+        Assert.Equal(5d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldTreatTextInRangeAsZeroAndNumericTextAsNumber()
+    {
+        sheet.Cells["A1"].Value = "abc"; // -> 0
+        sheet.Cells["A2"].Value = "15";  // -> 15
+        sheet.Cells["A3"].Value = 10;
+
+        sheet.Cells["B1"].Formula = "=MAXA(A1:A3)";
+
+        Assert.Equal(15d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldCountDirectLogicalAndTextArguments()
+    {
+        sheet.Cells["A1"].Formula = "=MAXA(1=1, \"7\", 1=2)"; // TRUE, "7", FALSE -> 7
+        Assert.Equal(7d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnZeroWhenNoValues()
+    {
+        sheet.Cells["A1"].Value = null; // empty
+        sheet.Cells["A2"].Value = "";  // empty string -> Empty
+
+        sheet.Cells["B1"].Formula = "=MAXA(A1:A2)";
+
+        Assert.Equal(0d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldPropagateErrors()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 0;
+        sheet.Cells["A3"].Formula = "=A1/A2"; // #DIV/0!
+
+        sheet.Cells["B1"].Formula = "=MAXA(A1:A3)";
+
+        Assert.Equal(CellError.Div0, sheet.Cells["B1"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/MaxFunctionTests.cs

@@ -0,0 +1,69 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class MaxFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldReturnLargestValueFromNumbers()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 7;
+        sheet.Cells["A3"].Value = 9;
+        sheet.Cells["A4"].Value = 27;
+        sheet.Cells["A5"].Value = 2;
+
+        sheet.Cells["B1"].Formula = "=MAX(A1:A5)";
+
+        Assert.Equal(27d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnLargestValueFromRangeAndLiteral()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 7;
+        sheet.Cells["A3"].Value = 9;
+        sheet.Cells["A4"].Value = 27;
+        sheet.Cells["A5"].Value = 2;
+
+        sheet.Cells["B1"].Formula = "=MAX(A1:A5,30)";
+
+        Assert.Equal(30d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldIgnoreNonNumericInRange()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "text";
+        sheet.Cells["A3"].Value = true;
+        sheet.Cells["A4"].Value = 27;
+        sheet.Cells["A5"].Value = null;
+
+        sheet.Cells["B1"].Formula = "=MAX(A1:A5)";
+
+        Assert.Equal(27d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldTreatDirectLogicalAndNumericStringsAsNumbers()
+    {
+        sheet.Cells["A1"].Formula = "=MAX(\"15\", 5, 10)";
+        Assert.Equal(15d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnZeroWhenNoNumbers()
+    {
+        sheet.Cells["A1"].Value = "a";
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Formula = "=MAX(A1:A2)";
+
+        Assert.Equal(0d, sheet.Cells["A3"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/MidFunctionTests.cs

@@ -0,0 +1,51 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class MidFunctionTests
+{
+    [Fact]
+    public void Mid_Start1_Take5()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "Fluid Flow"; // length 10
+        sheet.Cells["B1"].Formula = "=MID(A2,1,5)";
+        Assert.Equal("Fluid", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Mid_Start7_Take20_Clamped()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "Fluid Flow"; // length 10
+        sheet.Cells["B1"].Formula = "=MID(A2,7,20)";
+        Assert.Equal("Flow", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Mid_StartBeyondLength_ReturnsEmpty()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "Fluid Flow"; // length 10
+        sheet.Cells["B1"].Formula = "=MID(A2,20,5)";
+        Assert.Equal(string.Empty, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Mid_StartLessThan1_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "Fluid Flow";
+        sheet.Cells["B1"].Formula = "=MID(A2,0,5)";
+        Assert.Equal(CellError.Value, sheet.Cells["B1"].Data.GetValueOrDefault<CellError>());
+    }
+
+    [Fact]
+    public void Mid_NegativeNumChars_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "Fluid Flow";
+        sheet.Cells["B1"].Formula = "=MID(A2,1,-1)";
+        Assert.Equal(CellError.Value, sheet.Cells["B1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/MinAllFunctionTests.cs

@@ -0,0 +1,64 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class MinAllFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldEvaluateLogicalValuesInRange()
+    {
+        sheet.Cells["A1"].Value = true;   // 1
+        sheet.Cells["A2"].Value = false;  // 0
+        sheet.Cells["A3"].Value = 5;      // 5
+
+        sheet.Cells["B1"].Formula = "=MINA(A1:A3)";
+
+        Assert.Equal(0d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldTreatTextInRangeAsZeroAndNumericTextAsNumber()
+    {
+        sheet.Cells["A1"].Value = "abc"; // -> 0
+        sheet.Cells["A2"].Value = "15";  // -> 15
+        sheet.Cells["A3"].Value = 10;
+
+        sheet.Cells["B1"].Formula = "=MINA(A1:A3)";
+
+        Assert.Equal(0d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldCountDirectLogicalAndTextArguments()
+    {
+        sheet.Cells["A1"].Formula = "=MINA(1=1, \"7\", 1=2)"; // TRUE, "7", FALSE -> min is 0
+        Assert.Equal(0d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnZeroWhenNoValues()
+    {
+        sheet.Cells["A1"].Value = null; // empty
+        sheet.Cells["A2"].Value = "";  // empty string -> Empty
+
+        sheet.Cells["B1"].Formula = "=MINA(A1:A2)";
+
+        Assert.Equal(0d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldPropagateErrors()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 0;
+        sheet.Cells["A3"].Formula = "=A1/A2"; // #DIV/0!
+
+        sheet.Cells["B1"].Formula = "=MINA(A1:A3)";
+
+        Assert.Equal(CellError.Div0, sheet.Cells["B1"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/MinFunctionTests.cs

@@ -0,0 +1,69 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class MinFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldReturnSmallestValueFromNumbers()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 7;
+        sheet.Cells["A3"].Value = 9;
+        sheet.Cells["A4"].Value = 27;
+        sheet.Cells["A5"].Value = 2;
+
+        sheet.Cells["B1"].Formula = "=MIN(A1:A5)";
+
+        Assert.Equal(2d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnSmallestValueFromRangeAndLiteral()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 7;
+        sheet.Cells["A3"].Value = 9;
+        sheet.Cells["A4"].Value = 27;
+        sheet.Cells["A5"].Value = 2;
+
+        sheet.Cells["B1"].Formula = "=MIN(A1:A5,1)";
+
+        Assert.Equal(1d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldIgnoreNonNumericInRange()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = "text";
+        sheet.Cells["A3"].Value = true;
+        sheet.Cells["A4"].Value = 27;
+        sheet.Cells["A5"].Value = null;
+
+        sheet.Cells["B1"].Formula = "=MIN(A1:A5)";
+
+        Assert.Equal(10d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldTreatDirectNumericStringsAsNumbers()
+    {
+        sheet.Cells["A1"].Formula = "=MIN(\"15\", 5, 10)";
+        Assert.Equal(5d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnZeroWhenNoNumbers()
+    {
+        sheet.Cells["A1"].Value = "a";
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Formula = "=MIN(A1:A2)";
+
+        Assert.Equal(0d, sheet.Cells["A3"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/MinuteFunctionTests.cs

@@ -0,0 +1,34 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class MinuteFunctionTests
+{
+    [Fact]
+    public void Minute_FromFraction_ReturnsMinutes()
+    {
+        var sheet = new Sheet(10, 10);
+        // 0.78125 = 18:45 -> minutes 45
+        sheet.Cells["A1"].Data = CellData.FromNumber(0.78125);
+        sheet.Cells["B1"].Formula = "=MINUTE(A1)";
+        Assert.Equal(45, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Minute_FromDateTimeValue_ReturnsMinute()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Data = CellData.FromDate(new System.DateTime(2011, 7, 18, 7, 45, 0));
+        sheet.Cells["B2"].Formula = "=MINUTE(A2)";
+        Assert.Equal(45, sheet.Cells["B2"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Minute_FromDateOnly_ReturnsZero()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A3"].Data = CellData.FromDate(new System.DateTime(2012, 4, 21));
+        sheet.Cells["B3"].Formula = "=MINUTE(A3)";
+        Assert.Equal(0, sheet.Cells["B3"].Data.GetValueOrDefault<double>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/MonthFunctionTests.cs

@@ -0,0 +1,31 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class MonthFunctionTests
+{
+    [Fact]
+    public void Month_FromDateSerial_ReturnsMonth()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=MONTH(VALUE(\"2011-04-15\"))";
+        Assert.Equal(4, sheet.Cells["A1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Month_FromDateValue_ReturnsMonth()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2011, 4, 15));
+        sheet.Cells["B1"].Formula = "=MONTH(A1)";
+        Assert.Equal(4, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Month_InvalidText_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=MONTH(\"abc\")";
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/NotFunctionTests.cs

@@ -0,0 +1,200 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class NotFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithTrueValue()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Formula = "=NOT(A1)";
+
+        Assert.Equal(false, sheet.Cells["A2"].Value);
+    }
+    
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithEmptyStringAsError()
+    {
+        sheet.Cells["A1"].Value = "";
+        sheet.Cells["A2"].Formula = "=NOT(A1)";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithFalseValue()
+    {
+        sheet.Cells["A1"].Value = false;
+        sheet.Cells["A2"].Formula = "=NOT(A1)";
+
+        Assert.Equal(true, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithNumericValue()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Formula = "=NOT(A1)";
+
+        Assert.Equal(false, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithZeroValue()
+    {
+        sheet.Cells["A1"].Value = 0;
+        sheet.Cells["A2"].Formula = "=NOT(A1)";
+
+        Assert.Equal(true, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithStringValue()
+    {
+        sheet.Cells["A1"].Value = "test";
+        sheet.Cells["A2"].Formula = "=NOT(A1)";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithEmptyValue()
+    {
+        sheet.Cells["A2"].Formula = "=NOT(A1)";
+
+        Assert.Equal(true, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithComparison()
+    {
+        sheet.Cells["A1"].Value = 50;
+        sheet.Cells["A2"].Formula = "=NOT(A1>100)";
+
+        Assert.Equal(true, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithTrueComparison()
+    {
+        sheet.Cells["A1"].Value = 150;
+        sheet.Cells["A2"].Formula = "=NOT(A1>100)";
+
+        Assert.Equal(false, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForNotFunctionWithNoArguments()
+    {
+        sheet.Cells["A1"].Formula = "=NOT()";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForNotFunctionWithMultipleArguments()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Formula = "=NOT(A1,A2)";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithRangeExpression()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Formula = "=NOT(A1:A1)";
+
+        Assert.Equal(false, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithDecimalValue()
+    {
+        sheet.Cells["A1"].Value = 0.5m;
+        sheet.Cells["A2"].Formula = "=NOT(A1)";
+
+        Assert.Equal(false, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithNegativeValue()
+    {
+        sheet.Cells["A1"].Value = -5;
+        sheet.Cells["A2"].Formula = "=NOT(A1)";
+
+        Assert.Equal(false, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionInIfStatement()
+    {
+        sheet.Cells["A1"].Value = 50;
+        sheet.Cells["A2"].Formula = "=IF(NOT(A1>100),\"Valid\",\"Invalid\")";
+
+        Assert.Equal("Valid", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionInIfStatementWithFalseCondition()
+    {
+        sheet.Cells["A1"].Value = 150;
+        sheet.Cells["A2"].Formula = "=IF(NOT(A1>100),\"Valid\",\"Invalid\")";
+
+        Assert.Equal("Invalid", sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithProvidedExample1()
+    {
+        sheet.Cells["A2"].Value = 50;
+        sheet.Cells["A3"].Formula = "=NOT(A2>100)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithProvidedExample2()
+    {
+        sheet.Cells["A2"].Value = 50;
+        sheet.Cells["A3"].Formula = "=IF(AND(NOT(A2>1),NOT(A2<100)),A2,\"The value is out of range\")";
+
+        Assert.Equal("The value is out of range", sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithProvidedExample3()
+    {
+        sheet.Cells["A3"].Value = 100;
+        sheet.Cells["A4"].Formula = "=IF(OR(NOT(A3<0),NOT(A3>50)),A3,\"The value is out of range\")";
+
+        Assert.Equal(100d, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithNestedLogicalFunctions()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Formula = "=NOT(AND(A1,A2))";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateNotFunctionWithOrFunction()
+    {
+        sheet.Cells["A1"].Value = false;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Formula = "=NOT(OR(A1,A2))";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/NowFunctionTests.cs

@@ -0,0 +1,33 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class NowFunctionTests
+{
+    [Fact]
+    public void Now_ReturnsCurrentDateTime()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=NOW()";
+        var dt = sheet.Cells["A1"].Data.GetValueOrDefault<System.DateTime>();
+        Assert.Equal(System.DateTime.Today, dt.Date);
+    }
+
+    [Fact]
+    public void Now_MinusToday_IsFractionalDayBetween0And1()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=NOW()-TODAY()";
+        var serial = sheet.Cells["A1"].Data.GetValueOrDefault<double>();
+        Assert.True(serial >= 0 && serial < 1);
+    }
+
+    [Fact]
+    public void Now_PlusSevenDays_MinusToday_IsBetweenSevenAndEight()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=NOW()+7 - TODAY()";
+        var serial = sheet.Cells["A1"].Data.GetValueOrDefault<double>();
+        Assert.True(serial >= 7 && serial < 8);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/OrFunctionTests.cs

@@ -0,0 +1,216 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class OrFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithAllTrueValues()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Value = true;
+        sheet.Cells["A3"].Formula = "=OR(A1,A2)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithOneTrueValue()
+    {
+        sheet.Cells["A1"].Value = true;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Formula = "=OR(A1,A2)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithAllFalseValues()
+    {
+        sheet.Cells["A1"].Value = false;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Formula = "=OR(A1,A2)";
+
+        Assert.Equal(false, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithNumericValues()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Value = 10;
+        sheet.Cells["A3"].Formula = "=OR(A1>1,A2<100)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithZeroAsFalse()
+    {
+        sheet.Cells["A1"].Value = 0;
+        sheet.Cells["A2"].Value = 1;
+        sheet.Cells["A3"].Formula = "=OR(A1,A2)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithBothZeroAsFalse()
+    {
+        sheet.Cells["A1"].Value = 0;
+        sheet.Cells["A2"].Value = 0;
+        sheet.Cells["A3"].Formula = "=OR(A1,A2)";
+
+        Assert.Equal(false, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithNonZeroAsTrue()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Value = 10;
+        sheet.Cells["A3"].Formula = "=OR(A1,A2)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithStringValues()
+    {
+        sheet.Cells["A1"].Value = "test";
+        sheet.Cells["A2"].Value = "hello";
+        sheet.Cells["A3"].Formula = "=OR(A1,A2)";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithStringValueAndNumber()
+    {
+        sheet.Cells["A1"].Value = "2";
+        sheet.Cells["A2"].Value = "hello";
+        sheet.Cells["A3"].Formula = "=OR(A1,A2)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithEmptyStringAsFalse()
+    {
+        sheet.Cells["A2"].Value = "2";
+        sheet.Cells["A3"].Formula = "=OR(A1,A2)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithBothEmptyStringsAsFalse()
+    {
+        sheet.Cells["A3"].Formula = "=OR(A1,A2)";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithMultipleArguments()
+    {
+        sheet.Cells["A1"].Value = false;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Value = true;
+        sheet.Cells["A4"].Formula = "=OR(A1,A2,A3)";
+
+        Assert.Equal(true, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithAllFalseInMultipleArguments()
+    {
+        sheet.Cells["A1"].Value = false;
+        sheet.Cells["A2"].Value = false;
+        sheet.Cells["A3"].Value = false;
+        sheet.Cells["A4"].Formula = "=OR(A1,A2,A3)";
+
+        Assert.Equal(false, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForEmptyOrFunction()
+    {
+        sheet.Cells["A1"].Formula = "=OR()";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithRangeExpression()
+    {
+        sheet.Cells["A1"].Value = false;
+        sheet.Cells["A2"].Value = true;
+        sheet.Cells["A3"].Formula = "=OR(A1:A2)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithMixedTypes()
+    {
+        sheet.Cells["A1"].Value = 0;
+        sheet.Cells["A2"].Value = "";
+        sheet.Cells["A3"].Value = true;
+        sheet.Cells["A4"].Formula = "=OR(A1,A2,A3)";
+
+        Assert.Equal(true, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionInIfStatement()
+    {
+        sheet.Cells["A1"].Value = 5;
+        sheet.Cells["A2"].Value = 10;
+        sheet.Cells["A3"].Formula = "=IF(OR(A1>1,A2<100),A1,\"Out of range\")";
+
+        Assert.Equal(5d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionInIfStatementWithFalseCondition()
+    {
+        sheet.Cells["A1"].Value = 0;
+        sheet.Cells["A2"].Value = 150;
+        sheet.Cells["A3"].Formula = "=IF(OR(A1>1,A2<100),A1,\"Out of range\")";
+
+        Assert.Equal("Out of range", sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithProvidedExample1()
+    {
+        sheet.Cells["A2"].Value = 50;
+        sheet.Cells["A3"].Formula = "=OR(A2>1,A2<100)";
+
+        Assert.Equal(true, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithProvidedExample2()
+    {
+        sheet.Cells["A2"].Value = 5;
+        sheet.Cells["A3"].Value = 25;
+        sheet.Cells["A4"].Formula = "=IF(OR(A2>1,A2<100),A3,\"The value is out of range\")";
+
+        Assert.Equal(25d, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateOrFunctionWithProvidedExample3()
+    {
+        sheet.Cells["A2"].Value = 75;
+        sheet.Cells["A3"].Formula = "=IF(OR(A2<0,A2>50),A2,\"The value is out of range\")";
+
+        Assert.Equal(75d, sheet.Cells["A3"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/ProperFunctionTests.cs

@@ -0,0 +1,33 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class ProperFunctionTests
+{
+    [Fact]
+    public void Proper_TitleCase_Simple()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "this is a TITLE";
+        sheet.Cells["B1"].Formula = "=PROPER(A2)";
+        Assert.Equal("This Is A Title", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Proper_KeepsHyphenation()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A3"].Value = "2-way street";
+        sheet.Cells["B1"].Formula = "=PROPER(A3)";
+        Assert.Equal("2-Way Street", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Proper_AlnumBoundary()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A4"].Value = "76BudGet";
+        sheet.Cells["B1"].Formula = "=PROPER(A4)";
+        Assert.Equal("76Budget", sheet.Cells["B1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/RandBetweenFunctionTests.cs

@@ -0,0 +1,31 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class RandBetweenFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Theory]
+    [InlineData(1, 100)]
+    [InlineData(-1, 1)]
+    [InlineData(0, 0)]
+    public void RandBetween_ShouldReturnInclusiveRange(int bottom, int top)
+    {
+        static string Tok(int n) => n < 0 ? $"0{n}" : n.ToString();
+        sheet.Cells["A1"].Formula = $"=RANDBETWEEN({Tok(bottom)},{Tok(top)})";
+        var v = sheet.Cells["A1"].Value;
+        Assert.IsType<double>(v); // numeric stored as double
+        var d = (double)v;
+        Assert.True(d >= bottom && d <= top);
+    }
+
+    [Fact]
+    public void RandBetween_ShouldReturnNumError_WhenBottomGreaterThanTop()
+    {
+        sheet.Cells["A1"].Formula = "=RANDBETWEEN(5,1)";
+        Assert.Equal(CellError.Num, sheet.Cells["A1"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/RandFunctionTests.cs

@@ -0,0 +1,36 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class RandFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void Rand_ShouldReturnInRangeZeroToOneExclusiveOfOne()
+    {
+        sheet.Cells["A1"].Formula = "=RAND()";
+        var v = sheet.Cells["A1"].Value;
+        Assert.IsType<double>(v);
+        var d = (double)v;
+        Assert.True(d >= 0d && d < 1d);
+    }
+
+    [Fact]
+    public void Rand_RecalculatesOnFormulaReassignment()
+    {
+        sheet.Cells["A1"].Formula = "=RAND()";
+        var d1 = (double)sheet.Cells["A1"].Value;
+        sheet.Cells["A1"].Formula = "=RAND()"; // force recalc
+        var d2 = (double)sheet.Cells["A1"].Value;
+        // It's possible (though unlikely) to be equal; allow a retry window
+        if (d1 == d2)
+        {
+            sheet.Cells["A1"].Formula = "=RAND()";
+            d2 = (double)sheet.Cells["A1"].Value;
+        }
+        Assert.True(d1 != d2 || (d1 >= 0d && d1 < 1d));
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/RangeSelectionItemTests.cs

@@ -0,0 +1,132 @@
+using Bunit;
+using System.Linq;
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class RangeSelectionItemTests : TestContext
+{
+    private readonly Sheet sheet = new(4, 4);
+
+    [Fact]
+    public void RangeSelectionItem_ShouldCalculateCorrectMaskForMergedCells()
+    {
+        // Arrange
+        var mergedRange = RangeRef.Parse("B1:C1");
+        sheet.MergedCells.Add(mergedRange);
+        
+        // Select a range that overlaps with the merged cell
+        var selectionRange = RangeRef.Parse("A1:D1");
+        sheet.Selection.Select(selectionRange);
+        
+        var context = new MockVirtualGridContext();
+
+        // Act
+        var cut = RenderComponent<RangeSelectionItem>(parameters => parameters
+            .Add(p => p.Range, selectionRange)
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Cell, sheet.Selection.Cell) // This should be A1 (the active cell)
+            .Add(p => p.Context, context));
+
+        // Assert
+        var element = cut.Find(".rz-spreadsheet-selection-range");
+        Assert.NotNull(element);
+        
+        // The style should include mask properties that account for the merged cell
+        var style = element.GetAttribute("style");
+        Assert.NotNull(style);
+        Assert.Contains("mask-size", style);
+        Assert.Contains("mask-position", style);
+    }
+
+    [Fact]
+    public void RangeSelectionItem_ShouldHandleNonMergedCellsCorrectly()
+    {
+        // Arrange
+        var selectionRange = RangeRef.Parse("A1:B2");
+        sheet.Selection.Select(selectionRange);
+        
+        var context = new MockVirtualGridContext();
+
+        // Act
+        var cut = RenderComponent<RangeSelectionItem>(parameters => parameters
+            .Add(p => p.Range, selectionRange)
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Cell, sheet.Selection.Cell)
+            .Add(p => p.Context, context));
+
+        // Assert
+        var element = cut.Find(".rz-spreadsheet-selection-range");
+        Assert.NotNull(element);
+        
+        var style = element.GetAttribute("style");
+        Assert.NotNull(style);
+        Assert.Contains("transform", style);
+        Assert.Contains("width", style);
+        Assert.Contains("height", style);
+    }
+
+    [Fact]
+    public void RangeSelectionItem_ShouldHandleMergedCellsAcrossFrozenColumnBoundary()
+    {
+        // Arrange
+        sheet.Columns.Frozen = 1; // Freeze first column
+        var mergedRange = RangeRef.Parse("A1:B1"); // Merged cell spans across frozen boundary
+        sheet.MergedCells.Add(mergedRange);
+        
+        // Select the merged cell
+        sheet.Selection.Select(mergedRange);
+        
+        var context = new MockVirtualGridContext();
+
+        // Get the split ranges (frozen and non-frozen parts)
+        var ranges = sheet.GetRanges(mergedRange).ToList();
+        Assert.Equal(2, ranges.Count); // Should be split into 2 parts
+
+        // Test the frozen part (A1:A1)
+        var frozenRange = ranges.First(r => r.FrozenColumn);
+        var frozenCut = RenderComponent<RangeSelectionItem>(parameters => parameters
+            .Add(p => p.Range, frozenRange.Range)
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Cell, sheet.Selection.Cell)
+            .Add(p => p.Context, context)
+            .Add(p => p.FrozenColumn, frozenRange.FrozenColumn)
+            .Add(p => p.FrozenRow, frozenRange.FrozenRow)
+            .Add(p => p.Top, frozenRange.Top)
+            .Add(p => p.Left, frozenRange.Left)
+            .Add(p => p.Bottom, frozenRange.Bottom)
+            .Add(p => p.Right, frozenRange.Right));
+
+        var frozenElement = frozenCut.Find(".rz-spreadsheet-selection-range");
+        Assert.NotNull(frozenElement);
+        Assert.Contains("rz-spreadsheet-frozen-column", frozenElement.ClassName);
+        
+        var frozenStyle = frozenElement.GetAttribute("style");
+        Assert.NotNull(frozenStyle);
+        Assert.Contains("mask-size", frozenStyle);
+        Assert.Contains("mask-position", frozenStyle);
+
+        // Test the non-frozen part (B1:B1)
+        var nonFrozenRange = ranges.First(r => !r.FrozenColumn);
+        var nonFrozenCut = RenderComponent<RangeSelectionItem>(parameters => parameters
+            .Add(p => p.Range, nonFrozenRange.Range)
+            .Add(p => p.Sheet, sheet)
+            .Add(p => p.Cell, sheet.Selection.Cell)
+            .Add(p => p.Context, context)
+            .Add(p => p.FrozenColumn, nonFrozenRange.FrozenColumn)
+            .Add(p => p.FrozenRow, nonFrozenRange.FrozenRow)
+            .Add(p => p.Top, nonFrozenRange.Top)
+            .Add(p => p.Left, nonFrozenRange.Left)
+            .Add(p => p.Bottom, nonFrozenRange.Bottom)
+            .Add(p => p.Right, nonFrozenRange.Right));
+
+        var nonFrozenElement = nonFrozenCut.Find(".rz-spreadsheet-selection-range");
+        Assert.NotNull(nonFrozenElement);
+        Assert.DoesNotContain("rz-spreadsheet-frozen-column", nonFrozenElement.ClassName);
+        
+        var nonFrozenStyle = nonFrozenElement.GetAttribute("style");
+        Assert.NotNull(nonFrozenStyle);
+        Assert.Contains("mask-size", nonFrozenStyle);
+        Assert.Contains("mask-position", nonFrozenStyle);
+    }
+} 

Radzen.Blazor.Tests/Spreadsheet/ReplaceFunctionTests.cs

@@ -0,0 +1,51 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class ReplaceFunctionTests
+{
+    [Fact]
+    public void Replace_Middle_WithAsterisk()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "abcdefghijk";
+        sheet.Cells["B1"].Formula = "=REPLACE(A2,6,5,\"*\")";
+        Assert.Equal("abcde*k", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Replace_LastTwoDigits_With10()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A3"].Value = "2009";
+        sheet.Cells["B1"].Formula = "=REPLACE(A3,3,2,\"10\")";
+        Assert.Equal("2010", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Replace_FirstThree_WithAt()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A4"].Value = "123456";
+        sheet.Cells["B1"].Formula = "=REPLACE(A4,1,3,\"@\")";
+        Assert.Equal("@456", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Replace_StartBeyond_Appends()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "abc";
+        sheet.Cells["B1"].Formula = "=REPLACE(A1,10,2,\"XYZ\")";
+        Assert.Equal("abcXYZ", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Replace_InvalidStartNum_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "abc";
+        sheet.Cells["B1"].Formula = "=REPLACE(A1,0,2,\"X\")";
+        Assert.Equal(CellError.Value, sheet.Cells["B1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/ReptFunctionTests.cs

@@ -0,0 +1,47 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class ReptFunctionTests
+{
+    [Fact]
+    public void Rept_Basic()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=REPT(\"*-\",3)";
+        Assert.Equal("*-*-*-", sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Rept_DashesTen()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=REPT(\"-\",10)";
+        Assert.Equal("----------", sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Rept_ZeroTimes_ReturnsEmpty()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=REPT(\"x\",0)";
+        Assert.Equal(string.Empty, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Rept_Negative_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=REPT(\"x\",-1)";
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Data.GetValueOrDefault<CellError>());
+    }
+
+    [Fact]
+    public void Rept_Overflow_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        // text length 2 * 20000 = 40000 > 32767
+        sheet.Cells["A1"].Formula = "=REPT(\"ab\",20000)";
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/RightFunctionTests.cs

@@ -0,0 +1,42 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class RightFunctionTests
+{
+    [Fact]
+    public void Right_WithCount_ReturnsSuffix()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "Sale Price";
+        sheet.Cells["B1"].Formula = "=RIGHT(A2,5)";
+        Assert.Equal("Price", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Right_OmittedCount_DefaultsToOne()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A3"].Value = "Stock Number";
+        sheet.Cells["B1"].Formula = "=RIGHT(A3)";
+        Assert.Equal("r", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Right_CountExceedsLength_ReturnsWhole()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "Hi";
+        sheet.Cells["B1"].Formula = "=RIGHT(A1,5)";
+        Assert.Equal("Hi", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Right_NegativeCount_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "Test";
+        sheet.Cells["B1"].Formula = "=RIGHT(A1,-1)";
+        Assert.Equal(CellError.Value, sheet.Cells["B1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/RoundDownFunctionTests.cs

@@ -0,0 +1,39 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class RoundDownFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldRoundDownToZeroDecimalPlaces()
+    {
+        sheet.Cells["A1"].Formula = "=ROUNDDOWN(3.2,0)";
+        Assert.Equal(3d, sheet.Cells["A1"].Value);
+
+        sheet.Cells["A2"].Formula = "=ROUNDDOWN(76.9,0)";
+        Assert.Equal(76d, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldRoundDownToSpecifiedDecimalPlaces()
+    {
+        sheet.Cells["A1"].Formula = "=ROUNDDOWN(3.14159,3)";
+        Assert.Equal(3.141, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldRoundDownNegativeNumbersTowardZero()
+    {
+        sheet.Cells["A1"].Formula = "=ROUNDDOWN(0-3.14159,1)";
+        Assert.Equal(-3.1, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldRoundDownToLeftOfDecimalWhenNegativeDigits()
+    {
+        sheet.Cells["A1"].Formula = "=ROUNDDOWN(31415.92654,0-2)";
+        Assert.Equal(31400d, sheet.Cells["A1"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/RoundFunctionTests.cs

@@ -0,0 +1,41 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class RoundFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldRoundToOneDecimalPlace()
+    {
+        sheet.Cells["A1"].Formula = "=ROUND(2.15,1)";
+        Assert.Equal(2.2, sheet.Cells["A1"].Value);
+
+        sheet.Cells["A2"].Formula = "=ROUND(2.149,1)";
+        Assert.Equal(2.1, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldRoundNegativeWithAwayFromZeroMidpoint()
+    {
+        sheet.Cells["A1"].Formula = "=ROUND(0-1.475,2)";
+        Assert.Equal(-1.48, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldRoundWithNegativeDigits()
+    {
+        sheet.Cells["A1"].Formula = "=ROUND(21.5,0-1)";
+        Assert.Equal(20d, sheet.Cells["A1"].Value);
+
+        sheet.Cells["A2"].Formula = "=ROUND(626.3,0-3)";
+        Assert.Equal(1000d, sheet.Cells["A2"].Value);
+
+        sheet.Cells["A3"].Formula = "=ROUND(1.98,0-1)";
+        Assert.Equal(0d, sheet.Cells["A3"].Value);
+
+        sheet.Cells["A4"].Formula = "=ROUND(0-50.55,0-2)";
+        Assert.Equal(-100d, sheet.Cells["A4"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/RoundUpFunctionTests.cs

@@ -0,0 +1,39 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class RoundUpFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldRoundUpToZeroDecimalPlaces()
+    {
+        sheet.Cells["A1"].Formula = "=ROUNDUP(3.2,0)";
+        Assert.Equal(4d, sheet.Cells["A1"].Value);
+
+        sheet.Cells["A2"].Formula = "=ROUNDUP(76.9,0)";
+        Assert.Equal(77d, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldRoundUpToSpecifiedDecimalPlaces()
+    {
+        sheet.Cells["A1"].Formula = "=ROUNDUP(3.14159,3)";
+        Assert.Equal(3.142, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldRoundUpNegativeNumbersAwayFromZero()
+    {
+        sheet.Cells["A1"].Formula = "=ROUNDUP(0-3.14159,1)";
+        Assert.Equal(-3.2, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldRoundUpToLeftOfDecimalWhenNegativeDigits()
+    {
+        sheet.Cells["A1"].Formula = "=ROUNDUP(31415.92654,0-2)";
+        Assert.Equal(31500d, sheet.Cells["A1"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/RowColumnCommandTests.cs

@@ -0,0 +1,301 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class RowColumnCommandTests
+{
+    [Fact]
+    public void DeleteRowsCommand_SingleRow_ExecuteAndUndo_RestoresState()
+    {
+        var sheet = new Sheet(4, 3);
+        sheet.Cells[0, 0].Value = "R1";
+        sheet.Cells[1, 0].Value = "R2";
+        sheet.Cells[2, 0].Value = "R3";
+        sheet.Cells[3, 0].Value = "R4";
+
+        var cmd = new DeleteRowsCommand(sheet, 1, 1);
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(3, sheet.RowCount);
+        Assert.Equal("R1", sheet.Cells[0, 0].Value);
+        Assert.Equal("R3", sheet.Cells[1, 0].Value);
+        Assert.Equal("R4", sheet.Cells[2, 0].Value);
+
+        sheet.Commands.Undo();
+
+        Assert.Equal(4, sheet.RowCount);
+        Assert.Equal("R1", sheet.Cells[0, 0].Value);
+        Assert.Equal("R2", sheet.Cells[1, 0].Value);
+        Assert.Equal("R3", sheet.Cells[2, 0].Value);
+        Assert.Equal("R4", sheet.Cells[3, 0].Value);
+    }
+
+    [Fact]
+    public void DeleteRowsCommand_ExecuteAndUndo_RestoresState()
+    {
+        var sheet = new Sheet(6, 3);
+        sheet.Cells[0, 0].Value = "R1";
+        sheet.Cells[1, 0].Value = "R2";
+        sheet.Cells[2, 0].Value = "R3";
+        sheet.Cells[3, 0].Value = "R4";
+        sheet.Cells[4, 0].Value = "R5";
+        sheet.Cells[5, 0].Value = "R6";
+
+        var cmd = new DeleteRowsCommand(sheet, 1, 3); // delete rows 2..4
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(3, sheet.RowCount);
+        Assert.Equal("R1", sheet.Cells[0, 0].Value);
+        Assert.Equal("R5", sheet.Cells[1, 0].Value);
+        Assert.Equal("R6", sheet.Cells[2, 0].Value);
+
+        sheet.Commands.Undo();
+        Assert.Equal(6, sheet.RowCount);
+        Assert.Equal("R1", sheet.Cells[0, 0].Value);
+        Assert.Equal("R2", sheet.Cells[1, 0].Value);
+        Assert.Equal("R3", sheet.Cells[2, 0].Value);
+        Assert.Equal("R4", sheet.Cells[3, 0].Value);
+        Assert.Equal("R5", sheet.Cells[4, 0].Value);
+        Assert.Equal("R6", sheet.Cells[5, 0].Value);
+    }
+
+    [Fact]
+    public void InsertRowAfterCommand_ExecuteAndUndo_RestoresState()
+    {
+        var sheet = new Sheet(4, 3);
+        sheet.Cells[1, 0].Value = 1d; // A2
+        sheet.Cells[1, 1].Formula = "=A2+10"; // B2
+
+        var cmd = new InsertRowAfterCommand(sheet, 1); // after row 1 -> insert at index 2
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(5, sheet.RowCount);
+        // Inserting after row 1 does not move row 1; A2 and B2 stay
+        Assert.Equal(1d, sheet.Cells[1, 0].Value);
+        Assert.Equal("=A2+10", sheet.Cells[1, 1].Formula);
+        Assert.Equal(11d, sheet.Cells[1, 1].Value);
+
+        sheet.Commands.Undo();
+
+        Assert.Equal(4, sheet.RowCount);
+        Assert.Equal(1d, sheet.Cells[1, 0].Value);
+        Assert.Equal("=A2+10", sheet.Cells[1, 1].Formula);
+    }
+
+    [Fact]
+    public void InsertRowBeforeCommand_ExecuteAndUndo_RestoresState()
+    {
+        var sheet = new Sheet(4, 3);
+        sheet.Cells[1, 0].Value = 1d; // A2
+        sheet.Cells[1, 1].Formula = "=A2+10"; // B2
+
+        var cmd = new InsertRowBeforeCommand(sheet, 1); // before row 1 -> insert at index 1
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(5, sheet.RowCount);
+        // value shifted down (A2 becomes A3)
+        Assert.Equal(1d, sheet.Cells[2, 0].Value);
+        // formula shifted down and reference updated A2->A3
+        Assert.Equal("=A3+10", sheet.Cells[2, 1].Formula);
+        Assert.Equal(11d, sheet.Cells[2, 1].Value);
+
+        sheet.Commands.Undo();
+
+        Assert.Equal(4, sheet.RowCount);
+        Assert.Equal(1d, sheet.Cells[1, 0].Value);
+        Assert.Equal("=A2+10", sheet.Cells[1, 1].Formula);
+    }
+
+    [Fact]
+    public void InsertRowAfterCommand_WithMultiSelection_InsertsAfterLastRow()
+    {
+        var sheet = new Sheet(6, 2);
+        // Mark rows with their index in A
+        for (int r = 0; r < 6; r++) sheet.Cells[r, 0].Value = r + 1;
+
+        // Simulate selection rows 1..3 (0-based), last is 3 -> insert after 3 at index 4
+        var cmd = new InsertRowAfterCommand(sheet, 3);
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(7, sheet.RowCount);
+        // Inserted row at index 4 is empty
+        Assert.Null(sheet.Cells[4, 0].Value);
+        // Row 5 takes previous row 4 value (5)
+        Assert.Equal(5d, sheet.Cells[5, 0].Value);
+        // Row 6 takes previous row 5 value (6)
+        Assert.Equal(6d, sheet.Cells[6, 0].Value);
+
+        sheet.Commands.Undo();
+        Assert.Equal(6, sheet.RowCount);
+        Assert.Equal(5d, sheet.Cells[4, 0].Value);
+    }
+
+    [Fact]
+    public void InsertRowBeforeCommand_WithMultiSelection_InsertsBeforeFirstRow()
+    {
+        var sheet = new Sheet(6, 2);
+        for (int r = 0; r < 6; r++) sheet.Cells[r, 0].Value = r + 1;
+
+        // Simulate selection rows 2..4 (first is 2) -> insert at index 2
+        var cmd = new InsertRowBeforeCommand(sheet, 2);
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(7, sheet.RowCount);
+        // Inserted row at index 2 is empty
+        Assert.Null(sheet.Cells[2, 0].Value);
+        // Row 3 takes previous row 2 value (3)
+        Assert.Equal(3d, sheet.Cells[3, 0].Value);
+
+        sheet.Commands.Undo();
+        Assert.Equal(6, sheet.RowCount);
+        Assert.Equal(3d, sheet.Cells[2, 0].Value);
+    }
+
+    [Fact]
+    public void InsertColumnAfterCommand_WithMultiSelection_InsertsAfterLastColumn()
+    {
+        var sheet = new Sheet(2, 6);
+        // Mark columns with their index in row 1
+        for (int c = 0; c < 6; c++) sheet.Cells[0, c].Value = c + 1;
+
+        // Simulate selection columns 1..3 (last is 3) -> insert after col 3 at index 4
+        var cmd = new InsertColumnAfterCommand(sheet, 3);
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(7, sheet.ColumnCount);
+        // Inserted column at index 4 is empty
+        Assert.Null(sheet.Cells[0, 4].Value);
+        // Column 5 takes previous column 4 value (5)
+        Assert.Equal(5d, sheet.Cells[0, 5].Value);
+
+        sheet.Commands.Undo();
+        Assert.Equal(6, sheet.ColumnCount);
+        Assert.Equal(5d, sheet.Cells[0, 4].Value);
+    }
+
+    [Fact]
+    public void InsertColumnBeforeCommand_WithMultiSelection_InsertsBeforeFirstColumn()
+    {
+        var sheet = new Sheet(2, 6);
+        for (int c = 0; c < 6; c++) sheet.Cells[0, c].Value = c + 1;
+
+        // Simulate selection columns 2..4 (first is 2) -> insert at index 2
+        var cmd = new InsertColumnBeforeCommand(sheet, 2);
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(7, sheet.ColumnCount);
+        // Inserted column at index 2 is empty
+        Assert.Null(sheet.Cells[0, 2].Value);
+        // Column 3 takes previous column 2 value (3)
+        Assert.Equal(3d, sheet.Cells[0, 3].Value);
+
+        sheet.Commands.Undo();
+        Assert.Equal(6, sheet.ColumnCount);
+        Assert.Equal(3d, sheet.Cells[0, 2].Value);
+    }
+
+    [Fact]
+    public void DeleteColumnsCommand_SingleColumn_ExecuteAndUndo_RestoresState()
+    {
+        var sheet = new Sheet(3, 4);
+        sheet.Cells[0, 0].Value = "A";
+        sheet.Cells[0, 1].Value = "B";
+        sheet.Cells[0, 2].Value = "C";
+        sheet.Cells[0, 3].Value = "D";
+
+        var cmd = new DeleteColumnsCommand(sheet, 1, 1);
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(3, sheet.ColumnCount);
+        Assert.Equal("A", sheet.Cells[0, 0].Value);
+        Assert.Equal("C", sheet.Cells[0, 1].Value);
+        Assert.Equal("D", sheet.Cells[0, 2].Value);
+
+        sheet.Commands.Undo();
+
+        Assert.Equal(4, sheet.ColumnCount);
+        Assert.Equal("A", sheet.Cells[0, 0].Value);
+        Assert.Equal("B", sheet.Cells[0, 1].Value);
+        Assert.Equal("C", sheet.Cells[0, 2].Value);
+        Assert.Equal("D", sheet.Cells[0, 3].Value);
+    }
+
+    [Fact]
+    public void DeleteColumnsCommand_ExecuteAndUndo_RestoresState()
+    {
+        var sheet = new Sheet(3, 6);
+        sheet.Cells[0, 0].Value = "A";
+        sheet.Cells[0, 1].Value = "B";
+        sheet.Cells[0, 2].Value = "C";
+        sheet.Cells[0, 3].Value = "D";
+        sheet.Cells[0, 4].Value = "E";
+        sheet.Cells[0, 5].Value = "F";
+
+        var cmd = new DeleteColumnsCommand(sheet, 1, 3); // delete B..D
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(3, sheet.ColumnCount);
+        Assert.Equal("A", sheet.Cells[0, 0].Value);
+        Assert.Equal("E", sheet.Cells[0, 1].Value);
+        Assert.Equal("F", sheet.Cells[0, 2].Value);
+
+        sheet.Commands.Undo();
+
+        Assert.Equal(6, sheet.ColumnCount);
+        Assert.Equal("A", sheet.Cells[0, 0].Value);
+        Assert.Equal("B", sheet.Cells[0, 1].Value);
+        Assert.Equal("C", sheet.Cells[0, 2].Value);
+        Assert.Equal("D", sheet.Cells[0, 3].Value);
+        Assert.Equal("E", sheet.Cells[0, 4].Value);
+        Assert.Equal("F", sheet.Cells[0, 5].Value);
+    }
+
+    [Fact]
+    public void InsertColumnBeforeCommand_ExecuteAndUndo_RestoresState()
+    {
+        var sheet = new Sheet(5, 5);
+        sheet.Cells[1, 0].Value = 1d;   // A2
+        sheet.Cells[1, 1].Formula = "=A2+10"; // B2
+
+        var cmd = new InsertColumnBeforeCommand(sheet, 0); // before A
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(6, sheet.ColumnCount);
+        // value shifted right (A2 becomes B2)
+        Assert.Equal(1d, sheet.Cells[1, 1].Value);
+        // formula shifted right and reference updated A2->B2
+        Assert.Equal("=B2+10", sheet.Cells[1, 2].Formula); // original B2 moved to C2
+        Assert.Equal(11d, sheet.Cells[1, 2].Value);
+
+        sheet.Commands.Undo();
+
+        Assert.Equal(5, sheet.ColumnCount);
+        Assert.Equal(1d, sheet.Cells[1, 0].Value);
+        Assert.Equal("=A2+10", sheet.Cells[1, 1].Formula);
+    }
+
+    [Fact]
+    public void InsertColumnAfterCommand_ExecuteAndUndo_RestoresState()
+    {
+        var sheet = new Sheet(5, 5);
+        sheet.Cells[1, 0].Value = 1d;   // A2
+        sheet.Cells[1, 1].Formula = "=A2+10"; // B2
+
+        var cmd = new InsertColumnAfterCommand(sheet, 0); // after A
+        Assert.True(sheet.Commands.Execute(cmd));
+
+        Assert.Equal(6, sheet.ColumnCount);
+        // value at A2 stays, but B2 moves to C2; formula references should update if referencing >= inserted column
+        Assert.Equal(1d, sheet.Cells[1, 0].Value);
+        Assert.Equal("=A2+10", sheet.Cells[1, 2].Formula); // original B2 moved to C2
+        Assert.Equal(11d, sheet.Cells[1, 2].Value);
+
+        sheet.Commands.Undo();
+
+        Assert.Equal(5, sheet.ColumnCount);
+        Assert.Equal(1d, sheet.Cells[1, 0].Value);
+        Assert.Equal("=A2+10", sheet.Cells[1, 1].Formula);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/RowFunctionTests.cs

@@ -0,0 +1,38 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class RowFunctionTests
+{
+    [Fact]
+    public void Row_OmittedReference_ReturnsCurrentRow()
+    {
+        var sheet = new Sheet(20, 10);
+        sheet.Cells["C10"].Formula = "=ROW()";
+        Assert.Equal(10d, sheet.Cells["C10"].Data.Value);
+    }
+
+    [Fact]
+    public void Row_SingleCellReference_ReturnsThatRow()
+    {
+        var sheet = new Sheet(20, 10);
+        sheet.Cells["A1"].Formula = "=ROW(C10)";
+        Assert.Equal(10d, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Row_RangeReference_ReturnsTopLeftRow()
+    {
+        var sheet = new Sheet(20, 10);
+        sheet.Cells["B2"].Formula = "=ROW(C10:E10)";
+        Assert.Equal(10d, sheet.Cells["B2"].Data.Value);
+    }
+
+    [Fact]
+    public void Row_RangeReference_MultiRowAndColumn_IsError()
+    {
+        var sheet = new Sheet(20, 10);
+        sheet.Cells["B2"].Formula = "=ROW(C10:D20)";
+        Assert.Equal(CellError.Value, sheet.Cells["B2"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/RowsFunctionTests.cs

@@ -0,0 +1,30 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class RowsFunctionTests
+{
+    [Fact]
+    public void Rows_Range_ReturnsRowCount()
+    {
+        var sheet = new Sheet(50, 20);
+        sheet.Cells["A1"].Formula = "=ROWS(C1:E4)";
+        Assert.Equal(4d, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Rows_SingleCell_ReturnsOne()
+    {
+        var sheet = new Sheet(50, 20);
+        sheet.Cells["A1"].Formula = "=ROWS(C10)";
+        Assert.Equal(1d, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Rows_SingleRowRange_ReturnsOne()
+    {
+        var sheet = new Sheet(50, 20);
+        sheet.Cells["A1"].Formula = "=ROWS(C10:E10)";
+        Assert.Equal(1d, sheet.Cells["A1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SearchFunctionTests.cs

@@ -0,0 +1,65 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SearchFunctionTests
+{
+    [Fact]
+    public void Search_SimpleCharacter()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=SEARCH(\"n\",\"printer\")";
+        Assert.Equal(4d, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Search_Substring()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=SEARCH(\"base\",\"database\")";
+        Assert.Equal(5d, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Search_StartNum_SkipsPrefix()
+    {
+        var sheet = new Sheet(10, 30);
+        sheet.Cells["A1"].Value = "AYF0093.YoungMensApparel";
+        sheet.Cells["B1"].Formula = "=SEARCH(\"Y\",A1,8)";
+        Assert.Equal(9d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Search_Wildcards_QuestionAndAsterisk()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "Profit Margin";
+        sheet.Cells["B1"].Formula = "=SEARCH(\"M*r?in\",A1)";
+        Assert.Equal(8d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Search_TildeEscapesWildcards()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = "a*?c";
+        sheet.Cells["B1"].Formula = "=SEARCH(\"~*~?\",A1)";
+        Assert.Equal(2d, sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Search_StartNumInvalid_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=SEARCH(\"e\",\"printer\",0)";
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Data.GetValueOrDefault<CellError>());
+    }
+
+    [Fact]
+    public void Search_NotFound_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=SEARCH(\"zzz\",\"printer\")";
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SecondFunctionTests.cs

@@ -0,0 +1,33 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SecondFunctionTests
+{
+    [Fact]
+    public void Second_FromDateTimeWithSeconds_ReturnsSeconds()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2020, 1, 1, 16, 48, 18));
+        sheet.Cells["B1"].Formula = "=SECOND(A1)";
+        Assert.Equal(18, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Second_FromDateTimeWithoutSeconds_ReturnsZero()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Data = CellData.FromDate(new System.DateTime(2020, 1, 1, 16, 48, 0));
+        sheet.Cells["B2"].Formula = "=SECOND(A2)";
+        Assert.Equal(0, sheet.Cells["B2"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Second_FromDateOnly_ReturnsZero()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A3"].Data = CellData.FromDate(new System.DateTime(2020, 1, 1));
+        sheet.Cells["B3"].Formula = "=SECOND(A3)";
+        Assert.Equal(0, sheet.Cells["B3"].Data.GetValueOrDefault<double>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SelectionCycleTests.cs

@@ -0,0 +1,287 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SelectionCycleTests
+{
+    readonly Sheet sheet = new(4, 4);
+
+    [Fact]
+    public void Should_MoveToTheNextHorizontalCell()
+    {
+        sheet.Selection.Select(RangeRef.Parse("A1:C1"));
+
+        var cell = sheet.Selection.Cycle(0, 1);
+
+        Assert.Equal("B1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:C1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToTheFirstCellInTheRangeWhenAtLastColumn()
+    {
+        sheet.Selection.Select(CellRef.Parse("C1"), RangeRef.Parse("A1:C1"));
+
+        var cell = sheet.Selection.Cycle(0, 1);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:C1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToTheNextRowInTheRangeWhenAtLastColumn()
+    {
+        sheet.Selection.Select(CellRef.Parse("C1"), RangeRef.Parse("A1:C2"));
+
+        var cell = sheet.Selection.Cycle(0, 1);
+
+        Assert.Equal("A2", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:C2"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToTheNextVerticalCell()
+    {
+        sheet.Selection.Select(RangeRef.Parse("A1:A3"));
+
+        var cell = sheet.Selection.Cycle(1, 0);
+
+        Assert.Equal("A2", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:A3"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToTheFirstCellInTheRangeWhenAtLastRow()
+    {
+        sheet.Selection.Select(CellRef.Parse("A3"), RangeRef.Parse("A1:A3"));
+
+        var cell = sheet.Selection.Cycle(1, 0);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:A3"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToTheNextColumnInTheRangeWhenAtLastRow()
+    {
+        sheet.Selection.Select(CellRef.Parse("A3"), RangeRef.Parse("A1:B3"));
+
+        var cell = sheet.Selection.Cycle(1, 0);
+
+        Assert.Equal("B1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:B3"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToThePreviousHorizontalCell()
+    {
+        sheet.Selection.Select(RangeRef.Parse("B1:C1"));
+
+        var cell = sheet.Selection.Cycle(0, -1);
+
+        Assert.Equal("C1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("B1:C1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToTheLastCellInTheRangeWhenAtFirstColumn()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"), RangeRef.Parse("A1:C1"));
+
+        var cell = sheet.Selection.Cycle(0, -1);
+
+        Assert.Equal("C1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:C1"), sheet.Selection.Range);
+    }
+
+
+    [Fact]
+    public void Should_MoveToThePreviousRowInTheRangeWhenAtFirstColumn()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"), RangeRef.Parse("A1:C2"));
+
+        var cell = sheet.Selection.Cycle(0, -1);
+
+        Assert.Equal("C2", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:C2"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToTheNextHorizontalCellIfOnlyOneCellIsSelected()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        var cell = sheet.Selection.Cycle(0, 1);
+
+        Assert.Equal("B1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("B1:B1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToTheNextVerticalCellIfOnlyOneCellIsSelected()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        var cell = sheet.Selection.Cycle(1, 0);
+
+        Assert.Equal("A2", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A2:A2"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToThePreviousHorizontalCellIfOnlyOneCellIsSelected()
+    {
+        sheet.Selection.Select(CellRef.Parse("B1"));
+
+        var cell = sheet.Selection.Cycle(0, -1);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:A1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveToThePreviousVerticalCellIfOnlyOneCellIsSelected()
+    {
+        sheet.Selection.Select(CellRef.Parse("A2"));
+
+        var cell = sheet.Selection.Cycle(-1, 0);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:A1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_StayInTheSameCellIfTheFirstCellIsSelectedAndMovingBackwards()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        var cell = sheet.Selection.Cycle(0, -1);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:A1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_StayInTheSameCellIfTheLastCellIsSelectedAndMovingForwards()
+    {
+        sheet.Selection.Select(CellRef.Parse("D4"));
+
+        var cell = sheet.Selection.Cycle(0, 1);
+
+        Assert.Equal("D4", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("D4:D4"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_StayInTheSameCellIfOnlyOneCellIsSelectedAndMovingUp()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        var cell = sheet.Selection.Cycle(-1, 0);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:A1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_StayInTheSameCellIfOnlyOneCellIsSelectedAndMovingDown()
+    {
+        sheet.Selection.Select(CellRef.Parse("D4"));
+
+        var cell = sheet.Selection.Cycle(1, 0);
+
+        Assert.Equal("D4", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("D4:D4"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_GoToTheFirstCellInTheSheetIfNoSelection()
+    {
+        var cell = sheet.Selection.Cycle(0, 1);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:A1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_GoToTheNextHorizontalMergedCellInTheSelectedRange()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(RangeRef.Parse("A1:D1"));
+
+        var cell = sheet.Selection.Cycle(0, 1);
+
+        Assert.Equal("B1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:D1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_GoToThePreviousHorizontalMergedCellInTheSelectedRange()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("D1"), RangeRef.Parse("A1:D1"));
+
+        var cell = sheet.Selection.Cycle(0, -1);
+
+        Assert.Equal("B1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:D1"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_GoToTheNextVerticalMergedCellInTheSelectedRange()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("A2:A3"));
+        sheet.Selection.Select(RangeRef.Parse("A1:A4"));
+
+        var cell = sheet.Selection.Cycle(1, 0);
+
+        Assert.Equal("A2", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:A4"), sheet.Selection.Range);
+    }
+    [Fact]
+    public void Should_GoToThePreviousVerticalMergedCellInTheSelectedRange()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("A2:A3"));
+        sheet.Selection.Select(CellRef.Parse("A4"), RangeRef.Parse("A1:A4"));
+
+        var cell = sheet.Selection.Cycle(-1, 0);
+
+        Assert.Equal("A2", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("A1:A4"), sheet.Selection.Range);
+    }
+
+    [Fact]
+    public void Should_MoveFromMergedCellToNextCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+
+        var cell = sheet.Selection.Cycle(0, 1);
+
+        Assert.Equal("D1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+        Assert.Equal(RangeRef.Parse("D1:D1"), sheet.Selection.Range);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SelectionExtensionTests.cs

@@ -0,0 +1,445 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SelectionExtensionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void Extend_ShouldAppendNextHorizontalCellToRange()
+    {
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(0, 1);
+
+        Assert.Equal("B1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAppendNextVerticalCellToRange()
+    {
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(1, 0);
+
+        Assert.Equal("B1:B2", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractPreviousHorizontalCellFromRange()
+    {
+        sheet.Selection.Select(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("B1:B1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractPreviousVerticalCellFromRange()
+    {
+        sheet.Selection.Select(RangeRef.Parse("B1:B2"));
+        sheet.Selection.Extend(-1, 0);
+
+        Assert.Equal("B1:B1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAppendPreviousHorizontalCellToRange()
+    {
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("A1:B1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldFirstAppendAndThenSubtractNextHorizontalCell()
+    {
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(0, 1);
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("B1:B1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldFirstAppendAndThenSubtractPreviousHorizontalCell()
+    {
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(0, -1);
+        sheet.Selection.Extend(0, 1);
+
+        Assert.Equal("B1:B1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAppendPreviousVerticalCellToRange()
+    {
+        sheet.Selection.Select(CellRef.Parse("B2"));
+        sheet.Selection.Extend(-1, 0);
+
+        Assert.Equal("B1:B2", sheet.Selection.Range.ToString());
+        Assert.Equal("B2", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldFirstAppendAndThenSubtractVerticalCell()
+    {
+        sheet.Selection.Select(CellRef.Parse("B2"));
+        sheet.Selection.Extend(1, 0);
+        sheet.Selection.Extend(-1, 0);
+
+        Assert.Equal("B2:B2", sheet.Selection.Range.ToString());
+        Assert.Equal("B2", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Select_ShouldSelectTheWholeMergedCellRangeWhenTheStartIsUsed()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+
+        Assert.Equal("B1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Select_ShouldSelectTheWholeMergedCellRangeWhenTheEndIsUsed()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("C1"));
+
+        Assert.Equal("B1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddNextHorizontalCellAfterMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(0, 1);
+
+        Assert.Equal("B1:D1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddNextHorizontalCellAfterMergedCellAgain()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(0, 1);
+        sheet.Selection.Extend(0, 1);
+
+        Assert.Equal("B1:E1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddNextMergedCellAfterMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.MergedCells.Add(RangeRef.Parse("D1:E1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(0, 1);
+
+        Assert.Equal("B1:E1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractNextMergedCellAfterMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.MergedCells.Add(RangeRef.Parse("D1:E1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(0, 1);
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("B1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddPreviousMergedCellBeforeMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.MergedCells.Add(RangeRef.Parse("D1:E1"));
+        sheet.Selection.Select(CellRef.Parse("D1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("B1:E1", sheet.Selection.Range.ToString());
+        Assert.Equal("D1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractPreviousMergedCellBeforeMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.MergedCells.Add(RangeRef.Parse("D1:E1"));
+        sheet.Selection.Select(CellRef.Parse("D1"));
+        sheet.Selection.Extend(0, -1);
+        sheet.Selection.Extend(0, 1);
+
+        Assert.Equal("D1:E1", sheet.Selection.Range.ToString());
+        Assert.Equal("D1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddPreviousHorizontalMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("D1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("B1:D1", sheet.Selection.Range.ToString());
+        Assert.Equal("D1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubractPreviousMergedCellFromSelection()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("D1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("B1:D1", sheet.Selection.Range.ToString());
+        sheet.Selection.Extend(0, 1);
+
+        Assert.Equal("D1:D1", sheet.Selection.Range.ToString());
+        Assert.Equal("D1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractNextMergedCellFromSelection()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(RangeRef.Parse("A1:C1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("A1:A1", sheet.Selection.Range.ToString());
+        Assert.Equal("A1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractPreviousHorizontalCellBeforeMergedCellFromSelection()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Extend(0, -1);
+        Assert.Equal("A1:C1", sheet.Selection.Range.ToString());
+
+        sheet.Selection.Extend(0, 1);
+
+        Assert.Equal("B1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddPreviousHorizontalCellBeforeMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("A1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddNextVerticalCellAfterMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:B2"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(1, 0);
+
+        Assert.Equal("B1:B3", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddNextVerticalCellAfterMergedCellAgain()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:B2"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(1, 0);
+        sheet.Selection.Extend(1, 0);
+
+        Assert.Equal("B1:B4", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldHandleMergedCellsConsistentlyWhenMovingLeft()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("D1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("B1:D1", sheet.Selection.Range.ToString());
+        Assert.Equal("D1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldHandleMergedCellsConsistentlyWhenMovingLeftFromStart()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("A1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldHandleMergedCellsConsistentlyWhenMovingLeftFromEnd()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("C1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("A1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldHandleMergedCellsConsistentlyWhenMovingLeftFromEndAndThenRight()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("C1"));
+        sheet.Selection.Extend(0, -1);
+        sheet.Selection.Extend(0, 1);
+
+        Assert.Equal("B1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldHandleMergedCellsConsistentlyWhenMovingLeftFromMiddle()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:D1"));
+        sheet.Selection.Select(CellRef.Parse("C1"));
+        sheet.Selection.Extend(0, -1);
+
+        Assert.Equal("A1:D1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddNextMergedRowAfterMergedRow()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:B2"));
+        sheet.MergedCells.Add(RangeRef.Parse("B3:B4"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(1, 0);
+
+        Assert.Equal("B1:B4", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractNextMergedRowAfterMergedRow()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:B2"));
+        sheet.MergedCells.Add(RangeRef.Parse("B3:B4"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Extend(1, 0);
+        sheet.Selection.Extend(-1, 0);
+
+        Assert.Equal("B1:B2", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddPreviousMergedRowBeforeMergedRow()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:B2"));
+        sheet.MergedCells.Add(RangeRef.Parse("B3:B4"));
+        sheet.Selection.Select(CellRef.Parse("B3"));
+        sheet.Selection.Extend(-1, 0);
+
+        Assert.Equal("B1:B4", sheet.Selection.Range.ToString());
+        Assert.Equal("B3", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractPreviousMergedRowBeforeMergedRow()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:B2"));
+        sheet.MergedCells.Add(RangeRef.Parse("B3:B4"));
+        sheet.Selection.Select(CellRef.Parse("B3"));
+        sheet.Selection.Extend(-1, 0);
+        sheet.Selection.Extend(1, 0);
+
+        Assert.Equal("B3:B4", sheet.Selection.Range.ToString());
+        Assert.Equal("B3", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddPreviousVerticalMergedRow()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B2:B3"));
+        sheet.Selection.Select(CellRef.Parse("B4"));
+        sheet.Selection.Extend(-1, 0);
+
+        Assert.Equal("B2:B4", sheet.Selection.Range.ToString());
+        Assert.Equal("B4", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractPreviousMergedRowFromSelection()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B2:B3"));
+        sheet.Selection.Select(CellRef.Parse("B4"));
+        sheet.Selection.Extend(-1, 0);
+
+        Assert.Equal("B2:B4", sheet.Selection.Range.ToString());
+        sheet.Selection.Extend(1, 0);
+
+        Assert.Equal("B4:B4", sheet.Selection.Range.ToString());
+        Assert.Equal("B4", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractNextMergedRowFromSelection()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B2:B3"));
+        sheet.Selection.Select(RangeRef.Parse("B1:B3"));
+        sheet.Selection.Extend(-1, 0);
+
+        Assert.Equal("B1:B1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldSubtractPreviousVerticalCellBeforeMergedRowFromSelection()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B2:B3"));
+        sheet.Selection.Select(RangeRef.Parse("B2:B3"));
+        sheet.Selection.Extend(-1, 0);
+        Assert.Equal("B1:B3", sheet.Selection.Range.ToString());
+
+        sheet.Selection.Extend(1, 0);
+
+        Assert.Equal("B2:B3", sheet.Selection.Range.ToString());
+        Assert.Equal("B2", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Extend_ShouldAddPreviousVerticalCellBeforeMergedRow()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B2:B3"));
+        sheet.Selection.Select(CellRef.Parse("B2"));
+        sheet.Selection.Extend(-1, 0);
+
+        Assert.Equal("B1:B3", sheet.Selection.Range.ToString());
+        Assert.Equal("B2", sheet.Selection.Cell.ToString());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SelectionMergingTests.cs

@@ -0,0 +1,71 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SelectionMergingTests
+{
+    readonly Sheet sheet = new(4, 4);
+
+    [Fact]
+    public void Should_SelectAllHorizontalCellsBetweenTheCurrentCellAndTheNewOne()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+        sheet.Selection.Merge(CellRef.Parse("C1"));
+
+        Assert.Equal("A1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("A1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Should_SelectAllVerticalCellsBetweenTheCurrentCellAndTheNewOne()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+        sheet.Selection.Merge(CellRef.Parse("A3"));
+
+        Assert.Equal("A1:A3", sheet.Selection.Range.ToString());
+        Assert.Equal("A1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Should_ExtendRangeWhenMerginANewCell()
+    {
+        sheet.Selection.Select(RangeRef.Parse("A1:C1"));
+        sheet.Selection.Merge(CellRef.Parse("D2"));
+
+        Assert.Equal("A1:D2", sheet.Selection.Range.ToString());
+        Assert.Equal("A1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Should_AddTheEntireMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("A1"));
+        sheet.Selection.Merge(CellRef.Parse("B1"));
+
+        Assert.Equal("A1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("A1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Should_AddTheEntireMergedCellWhenSelectingIt()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+        sheet.Selection.Merge(CellRef.Parse("A1"));
+
+        Assert.Equal("A1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Should_ExpandSelectionToIncludeMergedCells()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("A1"));
+        sheet.Selection.Merge(CellRef.Parse("B2"));
+
+        Assert.Equal("A1:C2", sheet.Selection.Range.ToString());
+        Assert.Equal("A1", sheet.Selection.Cell.ToString());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SelectionMovingTests.cs

@@ -0,0 +1,155 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SelectionMovingTests
+{
+    readonly Sheet sheet = new(4, 4);
+
+    [Fact]
+    public void Should_MoveToTheNextHorizontalCell()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        var cell = sheet.Selection.Move(0, 1);
+
+        Assert.Equal("B1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_NotMoveToNextHorizontalCellWhenAlreadyAtLastColumn()
+    {
+        sheet.Selection.Select(CellRef.Parse("D1"));
+
+        var cell = sheet.Selection.Move(0, 1);
+
+        Assert.Equal("D1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_MoveToTheNextVerticalCell()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        var cell = sheet.Selection.Move(1, 0);
+
+        Assert.Equal("A2", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_NotMoveToNextVerticalCellWhenAlreadyAtLastRow()
+    {
+        sheet.Selection.Select(CellRef.Parse("A4"));
+
+        var cell = sheet.Selection.Move(1, 0);
+
+        Assert.Equal("A4", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_MoveToThePreviousHorizontalCell()
+    {
+        sheet.Selection.Select(CellRef.Parse("B1"));
+
+        var cell = sheet.Selection.Move(0, -1);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_NotMoveToPreviousHorizontalCellWhenAlreadyAtFirstColumn()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        var cell = sheet.Selection.Move(0, -1);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_MoveToThePreviousVerticalCell()
+    {
+        sheet.Selection.Select(CellRef.Parse("A2"));
+
+        var cell = sheet.Selection.Move(-1, 0);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_NotMoveToPreviousVerticalCellWhenAlreadyAtFirstRow()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        var cell = sheet.Selection.Move(-1, 0);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_MoveToNextHorizontalCellAfterMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("A1:B1"));
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        var cell = sheet.Selection.Move(0, 1);
+
+        Assert.Equal("C1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_MoveToNextVerticalCellAfterMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("A1:A2"));
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        var cell = sheet.Selection.Move(1, 0);
+
+        Assert.Equal("A3", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_MoveToPreviousHorizontalCellBeforeMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+
+        var cell = sheet.Selection.Move(0, -1);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_MoveToPreviousVerticalCellBeforeMergedCell()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("A2:A3"));
+        sheet.Selection.Select(CellRef.Parse("A2"));
+
+        var cell = sheet.Selection.Move(-1, 0);
+
+        Assert.Equal("A1", cell.ToString());
+        Assert.Equal(sheet.Selection.Cell, cell);
+    }
+
+    [Fact]
+    public void Should_MoveTheSelectedCellOnly()
+    {
+        sheet.Selection.Select(RangeRef.Parse("A1:C1"));
+
+        var cell = sheet.Selection.Move(0, 1);
+
+        Assert.Equal("B1", cell.ToString());
+        Assert.Equal("B1:B1", sheet.Selection.Range.ToString());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SelectionTests.cs

@@ -0,0 +1,75 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SelectionTests
+{
+    readonly Sheet sheet = new(4, 4);
+
+    [Fact]
+    public void Should_SelectSingleCell()
+    {
+        sheet.Selection.Select(CellRef.Parse("A1"));
+
+        Assert.Equal("A1", sheet.Selection.Cell.ToString());
+        Assert.Equal("A1:A1", sheet.Selection.Range.ToString());
+    }
+
+    [Fact]
+    public void Should_SelectRangeOfCells()
+    {
+        sheet.Selection.Select(RangeRef.Parse("A1:C3"));
+
+        Assert.Equal("A1", sheet.Selection.Cell.ToString());
+        Assert.Equal("A1", sheet.Selection.Range.Start.ToString());
+        Assert.Equal("C3", sheet.Selection.Range.End.ToString());
+        Assert.Equal("A1:C3", sheet.Selection.Range.ToString());
+    }
+
+    [Fact]
+    public void Should_SelectTheWholeMergedCellAsPartOfRange()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(RangeRef.Parse("A1:B1"));
+
+        Assert.Equal("A1:C1", sheet.Selection.Range.ToString());
+    }
+
+    [Fact]
+    public void Should_SelectTheWholeMergedCellByStart()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("B1"));
+
+        Assert.Equal("B1:C1", sheet.Selection.Range.ToString());
+    }
+
+    [Fact]
+    public void Should_SelectTheWholeMergedCellByEnd()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("C1"));
+
+        Assert.Equal("B1:C1", sheet.Selection.Range.ToString());
+    }
+
+    [Fact]
+    public void Should_SelectTheWholeMergedCellByEndAndRange()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("B1:C1"));
+        sheet.Selection.Select(CellRef.Parse("C1"), RangeRef.Parse("B1:C1"));
+
+        Assert.Equal("B1:C1", sheet.Selection.Range.ToString());
+        Assert.Equal("B1", sheet.Selection.Cell.ToString());
+    }
+
+    [Fact]
+    public void Should_SelectCompleteMergedCellRange()
+    {
+        sheet.MergedCells.Add(RangeRef.Parse("A1:D1"));
+        sheet.Selection.Select(RangeRef.Parse("A1:B2"));
+
+        Assert.Equal("A1:D2", sheet.Selection.Range.ToString());
+        Assert.Equal("A1", sheet.Selection.Cell.ToString());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SheetRangeTests.cs

@@ -0,0 +1,43 @@
+using System;
+using System.Linq;
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SheetRangeTests
+{
+    [Fact]
+    public void Range_Parse_ShouldParseValidRange()
+    {
+        var range = RangeRef.Parse("A1:B2");
+        
+        Assert.Equal(new CellRef(0, 0), range.Start);
+        Assert.Equal(new CellRef(1, 1), range.End);
+    }
+
+    [Fact]
+    public void Range_Parse_ShouldThrowOnInvalidRange()
+    {
+        Assert.Throws<ArgumentException>(() => RangeRef.Parse("A1:B2:C3"));
+    }
+
+    [Fact]
+    public void Range_GetCells_ShouldReturnAllCellsInRange()
+    {
+        var range = RangeRef.Parse("A1:B2");
+        var cells = range.GetCells().ToList();
+        
+        Assert.Equal(4, cells.Count);
+        Assert.Equal(new CellRef(0, 0), cells[0]); // A1
+        Assert.Equal(new CellRef(0, 1), cells[1]); // B1
+        Assert.Equal(new CellRef(1, 0), cells[2]); // A2
+        Assert.Equal(new CellRef(1, 1), cells[3]); // B2
+    }
+
+    [Fact]
+    public void Range_ToString_ShouldReturnA1Notation()
+    {
+        var range = new RangeRef(new CellRef(0, 0), new CellRef(1, 1));
+        Assert.Equal("A1:B2", range.ToString());
+    }
+} 

Radzen.Blazor.Tests/Spreadsheet/SmallFunctionTests.cs

@@ -0,0 +1,58 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SmallFunctionTests
+{
+    readonly Sheet sheet = new(12, 12);
+
+    [Fact]
+    public void ShouldReturn4thSmallestInFirstColumn()
+    {
+        sheet.Cells["A2"].Value = 3;
+        sheet.Cells["A3"].Value = 4;
+        sheet.Cells["A4"].Value = 5;
+        sheet.Cells["A5"].Value = 2;
+        sheet.Cells["A6"].Value = 3;
+        sheet.Cells["A7"].Value = 4;
+        sheet.Cells["A8"].Value = 6;
+        sheet.Cells["A9"].Value = 4;
+        sheet.Cells["A10"].Value = 7;
+
+        sheet.Cells["B1"].Formula = "=SMALL(A2:A10,4)";
+
+        Assert.Equal(4d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturn2ndSmallestInSecondColumn()
+    {
+        sheet.Cells["B2"].Value = 1;
+        sheet.Cells["B3"].Value = 4;
+        sheet.Cells["B4"].Value = 8;
+        sheet.Cells["B5"].Value = 3;
+        sheet.Cells["B6"].Value = 7;
+        sheet.Cells["B7"].Value = 12;
+        sheet.Cells["B8"].Value = 54;
+        sheet.Cells["B9"].Value = 8;
+        sheet.Cells["B10"].Value = 23;
+
+        sheet.Cells["C1"].Formula = "=SMALL(B2:B10,2)";
+
+        Assert.Equal(3d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldErrorForEmptyArrayOrInvalidK()
+    {
+        sheet.Cells["A1"].Formula = "=SMALL(A2:A2,1)"; // empty range
+        Assert.Equal(CellError.Num, sheet.Cells["A1"].Value);
+
+        sheet.Cells["A2"].Value = 5;
+        sheet.Cells["A3"].Formula = "=SMALL(A2:A2,0)"; // k <= 0
+        Assert.Equal(CellError.Num, sheet.Cells["A3"].Value);
+
+        sheet.Cells["A4"].Formula = "=SMALL(A2:A2,2)"; // k > count
+        Assert.Equal(CellError.Num, sheet.Cells["A4"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SortCommandTests.cs

@@ -0,0 +1,147 @@
+using System;
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SortCommandTests
+{
+    [Fact]
+    public void SortCommand_ShouldSortDataInAscendingOrder()
+    {
+        // Arrange
+        var sheet = new Sheet(5, 5);
+        var range = RangeRef.Parse("A1:A3");
+        
+        // Set up test data
+        sheet.Cells["A1"].Value = "Charlie";
+        sheet.Cells["A2"].Value = "Alice";
+        sheet.Cells["A3"].Value = "Bob";
+        
+        var command = new SortCommand(sheet, range, SortOrder.Ascending, 0);
+        
+        // Act
+        var result = command.Execute();
+        
+        // Assert
+        Assert.True(result);
+        Assert.Equal("Alice", sheet.Cells["A1"].Value);
+        Assert.Equal("Bob", sheet.Cells["A2"].Value);
+        Assert.Equal("Charlie", sheet.Cells["A3"].Value);
+    }
+    
+    [Fact]
+    public void SortCommand_ShouldSortDataInDescendingOrder()
+    {
+        // Arrange
+        var sheet = new Sheet(5, 5);
+        var range = RangeRef.Parse("A1:A3");
+        
+        // Set up test data
+        sheet.Cells["A1"].Value = "Alice";
+        sheet.Cells["A2"].Value = "Bob";
+        sheet.Cells["A3"].Value = "Charlie";
+        
+        var command = new SortCommand(sheet, range, SortOrder.Descending, 0);
+        
+        // Act
+        var result = command.Execute();
+        
+        // Assert
+        Assert.True(result);
+        Assert.Equal("Charlie", sheet.Cells["A1"].Value);
+        Assert.Equal("Bob", sheet.Cells["A2"].Value);
+        Assert.Equal("Alice", sheet.Cells["A3"].Value);
+    }
+    
+    [Fact]
+    public void SortCommand_ShouldRestoreOriginalOrderWhenUndone()
+    {
+        // Arrange
+        var sheet = new Sheet(5, 5);
+        var range = RangeRef.Parse("A1:A3");
+        
+        // Set up test data
+        sheet.Cells["A1"].Value = "Charlie";
+        sheet.Cells["A2"].Value = "Alice";
+        sheet.Cells["A3"].Value = "Bob";
+        
+        var command = new SortCommand(sheet, range, SortOrder.Ascending, 0);
+        
+        // Act
+        command.Execute();
+        command.Unexecute();
+        
+        // Assert
+        Assert.Equal("Charlie", sheet.Cells["A1"].Value);
+        Assert.Equal("Alice", sheet.Cells["A2"].Value);
+        Assert.Equal("Bob", sheet.Cells["A3"].Value);
+    }
+    
+    [Fact]
+    public void SortCommand_ShouldReturnFalseForInvalidRange()
+    {
+        // Arrange
+        var sheet = new Sheet(5, 5);
+        var command = new SortCommand(sheet, RangeRef.Invalid, SortOrder.Ascending, 0);
+        
+        // Act
+        var result = command.Execute();
+        
+        // Assert
+        Assert.False(result);
+    }
+    
+    [Fact]
+    public void SortCommand_ShouldPreserveCellFormatting()
+    {
+        // Arrange
+        var sheet = new Sheet(5, 5);
+        var range = RangeRef.Parse("A1:A2");
+        
+        // Set up test data with formatting
+        sheet.Cells["A1"].Value = "Charlie";
+        sheet.Cells["A1"].Format.Bold = true;
+        sheet.Cells["A2"].Value = "Alice";
+        sheet.Cells["A2"].Format.Italic = true;
+        
+        var command = new SortCommand(sheet, range, SortOrder.Ascending, 0);
+        
+        // Act
+        command.Execute();
+        command.Unexecute();
+        
+        // Assert
+        Assert.Equal("Charlie", sheet.Cells["A1"].Value);
+        Assert.True(sheet.Cells["A1"].Format.Bold);
+        Assert.Equal("Alice", sheet.Cells["A2"].Value);
+        Assert.True(sheet.Cells["A2"].Format.Italic);
+    }
+
+    [Fact]
+    public void SortCommand_ShouldWorkWithAutoFilterRange()
+    {
+        // Arrange
+        var sheet = new Sheet(5, 5);
+        var range = RangeRef.Parse("A1:B3");
+        
+        // Set up test data in a format similar to AutoFilter
+        sheet.Cells["A1"].Value = "Name";
+        sheet.Cells["B1"].Value = "Age";
+        sheet.Cells["A2"].Value = "Charlie";
+        sheet.Cells["B2"].Value = 30;
+        sheet.Cells["A3"].Value = "Alice";
+        sheet.Cells["B3"].Value = 25;
+        
+        var command = new SortCommand(sheet, range, SortOrder.Ascending, 0, skipHeaderRow: true);
+        
+        // Act
+        var result = command.Execute();
+        
+        // Assert
+        Assert.True(result);
+        Assert.Equal("Alice", sheet.Cells["A2"].Value);
+        Assert.Equal(25.0, sheet.Cells["B2"].Value);
+        Assert.Equal("Charlie", sheet.Cells["A3"].Value);
+        Assert.Equal(30.0, sheet.Cells["B3"].Value);
+    }
+} 

Radzen.Blazor.Tests/Spreadsheet/SortingTests.cs

@@ -0,0 +1,231 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SortingTests
+{
+    private readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void Should_SortStringsInAscendingOrder()
+    {
+        sheet.Cells[0, 0].Value = "C";
+        sheet.Cells[1, 0].Value = "A";
+        sheet.Cells[2, 0].Value = "B";
+
+        sheet.Sort(RangeRef.Parse("A1:A3"), SortOrder.Ascending);
+
+        Assert.Equal("A", sheet.Cells[0, 0].Value);
+        Assert.Equal("B", sheet.Cells[1, 0].Value);
+        Assert.Equal("C", sheet.Cells[2, 0].Value);
+    }
+
+    [Fact]
+    public void Should_SortStringsInDescendingOrder()
+    {
+        sheet.Cells[0, 0].Value = "C";
+        sheet.Cells[1, 0].Value = "A";
+        sheet.Cells[2, 0].Value = "B";
+
+        sheet.Sort(RangeRef.Parse("A1:A3"), SortOrder.Descending);
+
+        Assert.Equal("C", sheet.Cells[0, 0].Value);
+        Assert.Equal("B", sheet.Cells[1, 0].Value);
+        Assert.Equal("A", sheet.Cells[2, 0].Value);
+    }
+
+    [Fact]
+    public void Should_SortNumbersInDescendingOrder()
+    {
+        sheet.Cells[0, 0].Value = 1;
+        sheet.Cells[1, 0].Value = 3;
+        sheet.Cells[2, 0].Value = 2;
+
+        sheet.Sort(RangeRef.Parse("A1:A3"), SortOrder.Descending);
+
+        Assert.Equal(3d, sheet.Cells[0, 0].Value);
+        Assert.Equal(2d, sheet.Cells[1, 0].Value);
+        Assert.Equal(1d, sheet.Cells[2, 0].Value);
+    }
+
+    [Fact]
+    public void Should_SortFullRowsByColumnA()
+    {
+        sheet.Cells[0, 0].Value = "B"; sheet.Cells[0, 1].Value = "B2";
+        sheet.Cells[1, 0].Value = "A"; sheet.Cells[1, 1].Value = "A2";
+        sheet.Cells[2, 0].Value = "C"; sheet.Cells[2, 1].Value = "C2";
+
+        sheet.Sort(RangeRef.Parse("A1:B3"), SortOrder.Ascending);
+
+        Assert.Equal("A", sheet.Cells[0, 0].Value);
+        Assert.Equal("A2", sheet.Cells[0, 1].Value);
+        Assert.Equal("B", sheet.Cells[1, 0].Value);
+        Assert.Equal("B2", sheet.Cells[1, 1].Value);
+        Assert.Equal("C", sheet.Cells[2, 0].Value);
+        Assert.Equal("C2", sheet.Cells[2, 1].Value);
+    }
+
+    [Fact]
+    public void Should_IgnoreHeaderRowInSort()
+    {
+        sheet.Cells[0, 0].Value = "Header";
+        sheet.Cells[1, 0].Value = "C";
+        sheet.Cells[2, 0].Value = "A";
+        sheet.Cells[3, 0].Value = "B";
+
+        sheet.Sort(RangeRef.Parse("A2:A4"), SortOrder.Ascending);
+
+        Assert.Equal("Header", sheet.Cells[0, 0].Value); // header unchanged
+        Assert.Equal("A", sheet.Cells[1, 0].Value);
+        Assert.Equal("B", sheet.Cells[2, 0].Value);
+        Assert.Equal("C", sheet.Cells[3, 0].Value);
+    }
+
+    [Fact]
+    public void Should_SortOnlySelectedRange_NotWholeSheet()
+    {
+        sheet.Cells[0, 0].Value = "Z";
+        sheet.Cells[1, 0].Value = "X";
+        sheet.Cells[2, 0].Value = "Y";
+        sheet.Cells[3, 0].Value = "A";
+
+        sheet.Sort(RangeRef.Parse("A2:A4"), SortOrder.Ascending);
+
+        Assert.Equal("Z", sheet.Cells[0, 0].Value); // unchanged
+        Assert.Equal("A", sheet.Cells[1, 0].Value);
+        Assert.Equal("X", sheet.Cells[2, 0].Value);
+        Assert.Equal("Y", sheet.Cells[3, 0].Value);
+    }
+
+    [Fact]
+    public void Should_SortBlanksLastInAscendingOrder()
+    {
+        sheet.Cells[0, 0].Value = "B";
+        sheet.Cells[1, 0].Value = null; // blank
+        sheet.Cells[2, 0].Value = "A";
+
+        sheet.Sort(RangeRef.Parse("A1:A3"), SortOrder.Ascending);
+
+        Assert.Equal("A", sheet.Cells[0, 0].Value);
+        Assert.Equal("B", sheet.Cells[1, 0].Value);
+        Assert.Null(sheet.Cells[2, 0].Value);
+    }
+
+    [Fact]
+    public void Should_NotBreakDataAlignmentAcrossColumns()
+    {
+        sheet.Cells[0, 0].Value = "Charlie"; sheet.Cells[0, 1].Value = "30";
+        sheet.Cells[1, 0].Value = "Alice"; sheet.Cells[1, 1].Value = "25";
+        sheet.Cells[2, 0].Value = "Bob"; sheet.Cells[2, 1].Value = "20";
+
+        sheet.Sort(RangeRef.Parse("A1:B3"), SortOrder.Ascending);
+
+        Assert.Equal("Alice", sheet.Cells[0, 0].Value);
+        Assert.Equal(25d, sheet.Cells[0, 1].Value);
+        Assert.Equal("Bob", sheet.Cells[1, 0].Value);
+        Assert.Equal(20d, sheet.Cells[1, 1].Value);
+        Assert.Equal("Charlie", sheet.Cells[2, 0].Value);
+        Assert.Equal(30d, sheet.Cells[2, 1].Value);
+    }
+
+
+    [Fact]
+    public void Should_SortByAbsoluteColumnIndex()
+    {
+        // Data layout now starts at column B (index 1):
+        // | B (Name) | C (Age) | D (Dept) |
+        // |----------|---------|----------|
+        // | Charlie  | 42      | Dev      |
+        // | Alice    | 25      | HR       |
+        // | Bob      | 30      | Sales    |
+
+        sheet.Cells[0, 1].Value = "Charlie"; // B1
+        sheet.Cells[0, 2].Value = 42;        // C1
+        sheet.Cells[0, 3].Value = "Dev";     // D1
+
+        sheet.Cells[1, 1].Value = "Alice";   // B2
+        sheet.Cells[1, 2].Value = 25;        // C2
+        sheet.Cells[1, 3].Value = "HR";      // D2
+
+        sheet.Cells[2, 1].Value = "Bob";     // B3
+        sheet.Cells[2, 2].Value = 30;        // C3
+        sheet.Cells[2, 3].Value = "Sales";   // D3
+
+        // Sort range B1:D3 by **column C** (absolute index 2, "Age")
+        sheet.Sort(RangeRef.Parse("B1:D3"), SortOrder.Ascending, keyIndex: 2);
+
+        // Sorted order: Alice (25), Bob (30), Charlie (42)
+
+        Assert.Equal("Alice", sheet.Cells[0, 1].Value);
+        Assert.Equal(25d, sheet.Cells[0, 2].Value);
+        Assert.Equal("HR", sheet.Cells[0, 3].Value);
+
+        Assert.Equal("Bob", sheet.Cells[1, 1].Value);
+        Assert.Equal(30d, sheet.Cells[1, 2].Value);
+        Assert.Equal("Sales", sheet.Cells[1, 3].Value);
+
+        Assert.Equal("Charlie", sheet.Cells[2, 1].Value);
+        Assert.Equal(42d, sheet.Cells[2, 2].Value);
+        Assert.Equal("Dev", sheet.Cells[2, 3].Value);
+    }
+
+    [Fact]
+    public void Should_SortCellsWithRelativeFormulasCorrectly()
+    {
+        // Initial setup:
+        // A1:  2
+        // A2:  =A1 + 1   (should be 3)
+        // A3:  1
+
+        sheet.Cells[0, 0].Value = 2;           // A1
+        sheet.Cells[1, 0].Formula = "=A1 + 1"; // A2
+        sheet.Cells[2, 0].Value = 1;           // A3
+
+        // Confirm initial formula result
+        Assert.Equal(3d, sheet.Cells[1, 0].Value);
+
+        // Now sort A1:A3 in ascending order
+        sheet.Sort(RangeRef.Parse("A1:A3"), SortOrder.Ascending);
+
+        // The sorted order should be:
+        // A1:  1         (was A3)
+        // A2:  2         (was A1)
+        // A3:  =A1 + 1   (was A2)
+
+        Assert.Equal(1d, sheet.Cells[0, 0].Value);               // A1
+        Assert.Equal(2d, sheet.Cells[1, 0].Value);               // A2
+        Assert.Equal("=A1 + 1", sheet.Cells[2, 0].Formula);     // A3
+        Assert.Equal(2d, sheet.Cells[2, 0].Value);               // A3 evaluated: =1 + 1
+    }
+
+    [Fact]
+    public void Should_PlaceBlankValuesAtBottomInAscendingAndDescending()
+    {
+        sheet.Cells[0, 0].Value = 3;
+        sheet.Cells[1, 0].Value = null; // blank
+        sheet.Cells[2, 0].Value = 1;
+        sheet.Cells[3, 0].Value = 2;
+
+        // Sort ascending
+        sheet.Sort(RangeRef.Parse("A1:A4"), SortOrder.Ascending);
+
+        Assert.Equal(1d, sheet.Cells[0, 0].Value);
+        Assert.Equal(2d, sheet.Cells[1, 0].Value);
+        Assert.Equal(3d, sheet.Cells[2, 0].Value);
+        Assert.Null(sheet.Cells[3, 0].Value);
+
+        // Re-set original order
+        sheet.Cells[0, 0].Value = 3;
+        sheet.Cells[1, 0].Value = null;
+        sheet.Cells[2, 0].Value = 1;
+        sheet.Cells[3, 0].Value = 2;
+
+        // Sort descending
+        sheet.Sort(RangeRef.Parse("A1:A4"), SortOrder.Descending);
+
+        Assert.Equal(3d, sheet.Cells[0, 0].Value);
+        Assert.Equal(2d, sheet.Cells[1, 0].Value);
+        Assert.Equal(1d, sheet.Cells[2, 0].Value);
+        Assert.Null(sheet.Cells[3, 0].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SpreadsheetClipboardTests.cs

@@ -0,0 +1,60 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SpreadsheetClipboardTests
+{
+    [Fact]
+    public void Copy_Down_AdjustsRelative_KeepsAbsolute()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells[0, 0].Formula = "=A1";        // A1
+        sheet.PasteRange(sheet, RangeRef.Parse("A1"), CellRef.Parse("A2"), FormulaAdjustment.AdjustRelative);
+        Assert.Equal("=A2", sheet.Cells[1, 0].Formula);
+
+        sheet.Cells[0, 1].Formula = "=$A$1";     // B1
+        sheet.PasteRange(sheet, RangeRef.Parse("B1"), CellRef.Parse("B2"), FormulaAdjustment.AdjustRelative);
+        Assert.Equal("=$A$1", sheet.Cells[1, 1].Formula);
+    }
+
+    [Fact]
+    public void Copy_Right_AdjustsColumn_RetainsAbsoluteColumn()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells[0, 0].Formula = "=A1"; // A1
+        sheet.PasteRange(sheet, RangeRef.Parse("A1"), CellRef.Parse("B1"), FormulaAdjustment.AdjustRelative);
+        Assert.Equal("=B1", sheet.Cells[0, 1].Formula);
+
+        sheet.Cells[0, 1].Formula = "=$A1"; // B1 absolute column
+        sheet.PasteRange(sheet, RangeRef.Parse("B1"), CellRef.Parse("C1"), FormulaAdjustment.AdjustRelative);
+        Assert.Equal("=$A1", sheet.Cells[0, 2].Formula);
+    }
+
+    [Fact]
+    public void Cut_DoesNotAdjustFormula()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells[0, 0].Formula = "=A1"; // A1
+        sheet.Selection.Select(CellRef.Parse("A1"));
+        var clipboard = new SpreadsheetClipboard();
+        clipboard.Cut(sheet);
+        clipboard.Paste(sheet, CellRef.Parse("B2"));
+        Assert.Equal("=A1", sheet.Cells[1, 1].Formula); // not adjusted
+        Assert.Null(sheet.Cells[0, 0].Formula);          // source cleared
+        Assert.Null(sheet.Cells[0, 0].Value);
+    }
+
+    [Fact]
+    public void Copy_AcrossSheets_AdjustsRelativeReferences()
+    {
+        var source = new Sheet(10, 10);
+        var target = new Sheet(10, 10);
+
+        source.Cells[0, 0].Formula = "=A1";
+
+        // Copy A1 from source to B2 in target
+        target.PasteRange(source, RangeRef.Parse("A1"), CellRef.Parse("B2"), FormulaAdjustment.AdjustRelative);
+
+        Assert.Equal("=B2", target.Cells[1, 1].Formula);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SubstituteFunctionTests.cs

@@ -0,0 +1,33 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SubstituteFunctionTests
+{
+    [Fact]
+    public void Substitute_AllOccurrences()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "Sales Data";
+        sheet.Cells["B1"].Formula = "=SUBSTITUTE(A2, \"Sales\", \"Cost\")";
+        Assert.Equal("Cost Data", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Substitute_FirstInstanceOnly()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A3"].Value = "Quarter 1, 2008";
+        sheet.Cells["B1"].Formula = "=SUBSTITUTE(A3, \"1\", \"2\", 1)";
+        Assert.Equal("Quarter 2, 2008", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Substitute_ThirdInstanceOnly()
+    {
+        var sheet = new Sheet(10, 20);
+        sheet.Cells["A4"].Value = "Quarter 1, 2011";
+        sheet.Cells["B1"].Formula = "=SUBSTITUTE(A4, \"1\", \"2\", 3)";
+        Assert.Equal("Quarter 1, 2012", sheet.Cells["B1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SubtotalFunctionTests.cs

@@ -0,0 +1,94 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SubtotalFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldSumWithCode9()
+    {
+        sheet.Cells["A2"].Value = 120;
+        sheet.Cells["A3"].Value = 10;
+        sheet.Cells["A4"].Value = 150;
+        sheet.Cells["A5"].Value = 23;
+
+        sheet.Cells["B1"].Formula = "=SUBTOTAL(9,A2:A5)";
+
+        Assert.Equal(303d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldAverageWithCode1()
+    {
+        sheet.Cells["A2"].Value = 120;
+        sheet.Cells["A3"].Value = 10;
+        sheet.Cells["A4"].Value = 150;
+        sheet.Cells["A5"].Value = 23;
+
+        sheet.Cells["B1"].Formula = "=SUBTOTAL(1,A2:A5)";
+
+        Assert.Equal(75.75, sheet.Cells["B1"].Value);
+    }
+    [Fact]
+    public void ShouldCountWithCode2()
+    {
+        sheet.Cells["A2"].Value = 120;
+        sheet.Cells["A3"].Value = "x"; // non-numeric, ignored by COUNT
+        sheet.Cells["A4"].Value = 150;
+        sheet.Cells["A5"].Value = null;
+
+        sheet.Cells["B1"].Formula = "=SUBTOTAL(2,A2:A5)";
+        Assert.Equal(2d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldCountAWithCode3()
+    {
+        sheet.Cells["A2"].Value = 120;
+        sheet.Cells["A3"].Value = "x";
+        sheet.Cells["A4"].Value = null;
+        sheet.Cells["A5"].Value = 23;
+
+        sheet.Cells["B1"].Formula = "=SUBTOTAL(3,A2:A5)";
+        Assert.Equal(3d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldMaxWithCode4()
+    {
+        sheet.Cells["A2"].Value = 10;
+        sheet.Cells["A3"].Value = 40;
+        sheet.Cells["A4"].Value = 30;
+        sheet.Cells["A5"].Value = 20;
+
+        sheet.Cells["B1"].Formula = "=SUBTOTAL(4,A2:A5)";
+        Assert.Equal(40d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldMinWithCode5()
+    {
+        sheet.Cells["A2"].Value = 10;
+        sheet.Cells["A3"].Value = 40;
+        sheet.Cells["A4"].Value = 30;
+        sheet.Cells["A5"].Value = 20;
+
+        sheet.Cells["B1"].Formula = "=SUBTOTAL(5,A2:A5)";
+        Assert.Equal(10d, sheet.Cells["B1"].Value);
+    }
+
+    [Fact]
+    public void ShouldRespectHiddenRowsWith109()
+    {
+        sheet.Cells["A2"].Value = 120;
+        sheet.Cells["A3"].Value = 10;
+        sheet.Cells["A4"].Value = 150;
+        sheet.Cells["A5"].Value = 20;
+        sheet.Rows.Hide(2); // hide row 3 (A3)
+
+        sheet.Cells["B1"].Formula = "=SUBTOTAL(109,A2:A5)";
+        Assert.Equal(290d, sheet.Cells["B1"].Value); // 120 + 150 + 20 (excludes hidden 10)
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/SumFunctionTests.cs

@@ -0,0 +1,73 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SumFunctionTests
+{
+    readonly Sheet sheet = new(5, 5);
+
+    [Fact]
+    public void ShouldEvaluateSumFunction()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A2"].Value = 2;
+        sheet.Cells["A3"].Formula = "=SUM(A1,A2)";
+
+        Assert.Equal(3d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumFunctionWithEmptyCells()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A3"].Formula = "=SUM(A1,A2)";
+
+        Assert.Equal(1d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumFunctionWithMultipleArguments()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A2"].Value = 2;
+        sheet.Cells["A3"].Value = 3;
+        sheet.Cells["A4"].Formula = "=SUM(A1,A2,A3)";
+
+        Assert.Equal(6d, sheet.Cells["A4"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForEmptySumFunction()
+    {
+        sheet.Cells["A1"].Formula = "=SUM()";
+
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldSumRangeOfCells()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A2"].Value = 2;
+        sheet.Cells["A3"].Formula = "=SUM(A1:A2)";
+
+        Assert.Equal(3d, sheet.Cells["A3"].Value);
+    }
+
+    [Fact]
+    public void ShouldSumNumbersOfDifferentTypes()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A2"].Value = 2.5;
+        sheet.Cells["A3"].Formula = "=SUM(A1,A2)";
+
+        Assert.Equal(3.5, sheet.Cells["A3"].Value);
+
+        sheet.Cells["A4"].Value = 2.5;
+        sheet.Cells["A5"].Formula = "=SUM(A4,A1)";
+
+        Assert.Equal(3.5, sheet.Cells["A5"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/SumIfFunctionTests.cs

@@ -0,0 +1,278 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class SumIfFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithNumericCriteria()
+    {
+        // Test data from Excel example
+        sheet.Cells["A1"].Value = 100000;
+        sheet.Cells["A2"].Value = 200000;
+        sheet.Cells["A3"].Value = 300000;
+        sheet.Cells["A4"].Value = 400000;
+        
+        sheet.Cells["B1"].Value = 7000;
+        sheet.Cells["B2"].Value = 14000;
+        sheet.Cells["B3"].Value = 21000;
+        sheet.Cells["B4"].Value = 28000;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A4,\">160000\",B1:B4)";
+
+        Assert.Equal(63000d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithoutSumRange()
+    {
+        // Test data from Excel example
+        sheet.Cells["A1"].Value = 100000;
+        sheet.Cells["A2"].Value = 200000;
+        sheet.Cells["A3"].Value = 300000;
+        sheet.Cells["A4"].Value = 400000;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A4,\">160000\")";
+
+        Assert.Equal(900000d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithExactMatch()
+    {
+        // Test data from Excel example
+        sheet.Cells["A1"].Value = 100000;
+        sheet.Cells["A2"].Value = 200000;
+        sheet.Cells["A3"].Value = 300000;
+        sheet.Cells["A4"].Value = 400000;
+        
+        sheet.Cells["B1"].Value = 7000;
+        sheet.Cells["B2"].Value = 14000;
+        sheet.Cells["B3"].Value = 21000;
+        sheet.Cells["B4"].Value = 28000;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A4,300000,B1:B4)";
+
+        Assert.Equal(21000d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithStringCriteria()
+    {
+        // Test data from Excel example
+        sheet.Cells["A1"].Value = "Vegetables";
+        sheet.Cells["A2"].Value = "Vegetables";
+        sheet.Cells["A3"].Value = "Fruits";
+        sheet.Cells["A4"].Value = "";
+        sheet.Cells["A5"].Value = "Vegetables";
+        sheet.Cells["A6"].Value = "Fruits";
+        
+        sheet.Cells["C1"].Value = 2300;
+        sheet.Cells["C2"].Value = 5500;
+        sheet.Cells["C3"].Value = 800;
+        sheet.Cells["C4"].Value = 400;
+        sheet.Cells["C5"].Value = 4200;
+        sheet.Cells["C6"].Value = 1200;
+
+        sheet.Cells["D1"].Formula = "=SUMIF(A1:A6,\"Fruits\",C1:C6)";
+
+        Assert.Equal(2000d, sheet.Cells["D1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithWildcardPattern()
+    {
+        // Test data from Excel example
+        sheet.Cells["A1"].Value = "Vegetables";
+        sheet.Cells["A2"].Value = "Vegetables";
+        sheet.Cells["A3"].Value = "Fruits";
+        sheet.Cells["A4"].Value = "";
+        sheet.Cells["A5"].Value = "Vegetables";
+        sheet.Cells["A6"].Value = "Fruits";
+        
+        sheet.Cells["B1"].Value = "Tomatoes";
+        sheet.Cells["B2"].Value = "Celery";
+        sheet.Cells["B3"].Value = "Oranges";
+        sheet.Cells["B4"].Value = "Butter";
+        sheet.Cells["B5"].Value = "Carrots";
+        sheet.Cells["B6"].Value = "Apples";
+        
+        sheet.Cells["C1"].Value = 2300;
+        sheet.Cells["C2"].Value = 5500;
+        sheet.Cells["C3"].Value = 800;
+        sheet.Cells["C4"].Value = 400;
+        sheet.Cells["C5"].Value = 4200;
+        sheet.Cells["C6"].Value = 1200;
+
+        sheet.Cells["D1"].Formula = "=SUMIF(B1:B6,\"*es\",C1:C6)";
+
+        Assert.Equal(4300d, sheet.Cells["D1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithEmptyCriteria()
+    {
+        // Test data from Excel example
+        sheet.Cells["A1"].Value = "Vegetables";
+        sheet.Cells["A2"].Value = "Vegetables";
+        sheet.Cells["A3"].Value = "Fruits";
+        sheet.Cells["A4"].Value = "";
+        sheet.Cells["A5"].Value = "Vegetables";
+        sheet.Cells["A6"].Value = "Fruits";
+        
+        sheet.Cells["C1"].Value = 2300;
+        sheet.Cells["C2"].Value = 5500;
+        sheet.Cells["C3"].Value = 800;
+        sheet.Cells["C4"].Value = 400;
+        sheet.Cells["C5"].Value = 4200;
+        sheet.Cells["C6"].Value = 1200;
+
+        sheet.Cells["D1"].Formula = "=SUMIF(A1:A6,\"\",C1:C6)";
+
+        Assert.Equal(400d, sheet.Cells["D1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithLessThanCriteria()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+        sheet.Cells["A4"].Value = 40;
+        
+        sheet.Cells["B1"].Value = 100;
+        sheet.Cells["B2"].Value = 200;
+        sheet.Cells["B3"].Value = 300;
+        sheet.Cells["B4"].Value = 400;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A4,\"<25\",B1:B4)";
+
+        Assert.Equal(300d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithGreaterThanOrEqualCriteria()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+        sheet.Cells["A4"].Value = 40;
+        
+        sheet.Cells["B1"].Value = 100;
+        sheet.Cells["B2"].Value = 200;
+        sheet.Cells["B3"].Value = 300;
+        sheet.Cells["B4"].Value = 400;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A4,\">=25\",B1:B4)";
+
+        Assert.Equal(700d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithNotEqualCriteria()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+        sheet.Cells["A4"].Value = 40;
+        
+        sheet.Cells["B1"].Value = 100;
+        sheet.Cells["B2"].Value = 200;
+        sheet.Cells["B3"].Value = 300;
+        sheet.Cells["B4"].Value = 400;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A4,\"<>20\",B1:B4)";
+
+        Assert.Equal(800d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithQuestionMarkWildcard()
+    {
+        sheet.Cells["A1"].Value = "cat";
+        sheet.Cells["A2"].Value = "bat";
+        sheet.Cells["A3"].Value = "rat";
+        sheet.Cells["A4"].Value = "goat";
+        
+        sheet.Cells["B1"].Value = 10;
+        sheet.Cells["B2"].Value = 20;
+        sheet.Cells["B3"].Value = 30;
+        sheet.Cells["B4"].Value = 40;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A4,\"?at\",B1:B4)";
+
+        Assert.Equal(60d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldEvaluateSumIfFunctionWithEscapedWildcards()
+    {
+        sheet.Cells["A1"].Value = "*";
+        sheet.Cells["A2"].Value = "?";
+        sheet.Cells["A3"].Value = "test";
+        
+        sheet.Cells["B1"].Value = 10;
+        sheet.Cells["B2"].Value = 20;
+        sheet.Cells["B3"].Value = 30;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A3,\"~*\",B1:B3)";
+
+        Assert.Equal(10d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForInvalidArgumentCount()
+    {
+        sheet.Cells["A1"].Formula = "=SUMIF(A2)";
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Value);
+
+        sheet.Cells["A2"].Formula = "=SUMIF(A3,A4,A5,A6)";
+        Assert.Equal(CellError.Value, sheet.Cells["A2"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnValueErrorForMismatchedRangeSizes()
+    {
+        sheet.Cells["A1"].Value = 1;
+        sheet.Cells["A2"].Value = 2;
+        sheet.Cells["B1"].Value = 10;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A2,\">0\",B1)";
+
+        Assert.Equal(CellError.Value, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldHandleEmptyCellsInSumRange()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+        
+        // B2 is empty
+        sheet.Cells["B1"].Value = 100;
+        sheet.Cells["B3"].Value = 300;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A3,\">15\",B1:B3)";
+
+        Assert.Equal(300d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldHandleNonNumericValuesInSumRange()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+        
+        sheet.Cells["B1"].Value = 100;
+        sheet.Cells["B2"].Value = "text"; // Non-numeric
+        sheet.Cells["B3"].Value = 300;
+
+        sheet.Cells["C1"].Formula = "=SUMIF(A1:A3,\">15\",B1:B3)";
+
+        Assert.Equal(300d, sheet.Cells["C1"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/TextFunctionTests.cs

@@ -0,0 +1,53 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class TextFunctionTests
+{
+    [Fact]
+    public void Text_Currency_Thousands_TwoDecimals()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = 1234.567;
+        sheet.Cells["B1"].Formula = "=TEXT(A1,\"$#,##0.00\")";
+        Assert.Equal("$1,234.57", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Text_Date_MMDDYY()
+    {
+        var sheet = new Sheet(10, 10);
+        var dt = new System.DateTime(2012, 3, 14);
+        sheet.Cells["A1"].Value = dt;
+        sheet.Cells["B1"].Formula = "=TEXT(A1,\"MM/DD/YY\")";
+        Assert.Equal("03/14/12", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Text_Time_12h_AMPM()
+    {
+        var sheet = new Sheet(10, 10);
+        var dt = new System.DateTime(2020, 1, 1, 13, 29, 0);
+        sheet.Cells["A1"].Value = dt;
+        sheet.Cells["B1"].Formula = "=TEXT(A1,\"H:MM AM/PM\")";
+        Assert.Equal("1:29 PM", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Text_Percent_OneDecimal()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = 0.285;
+        sheet.Cells["B1"].Formula = "=TEXT(A1,\"0.0%\")";
+        Assert.Equal("28.5%", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Text_LeadingZeros()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Value = 1234;
+        sheet.Cells["B1"].Formula = "=TEXT(A1,\"0000000\")";
+        Assert.Equal("0001234", sheet.Cells["B1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/TextJoinFunctionTests.cs

@@ -0,0 +1,57 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class TextJoinFunctionTests
+{
+    [Fact]
+    public void TextJoin_Literals_IgnoreEmptyTrue()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=TEXTJOIN(\" \",TRUE,\"The\",\"sun\",\"will\",\"come\",\"up\",\"tomorrow.\")";
+        Assert.Equal("The sun will come up tomorrow.", sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void TextJoin_Range_CommaSpace_IgnoreEmptyTrue()
+    {
+        var sheet = new Sheet(20, 10);
+        // A2:A8 values
+        sheet.Cells["A2"].Value = "US Dollar";
+        sheet.Cells["A3"].Value = "Australian Dollar";
+        sheet.Cells["A4"].Value = "Chinese Yuan";
+        sheet.Cells["A5"].Value = "Hong Kong Dollar";
+        sheet.Cells["A6"].Value = "Israeli Shekel";
+        sheet.Cells["A7"].Value = "South Korean Won";
+        sheet.Cells["A8"].Value = "Russian Ruble";
+        sheet.Cells["B1"].Formula = "=TEXTJOIN(\", \", TRUE, A2:A8)";
+        var result = sheet.Cells["B1"].Data.GetValueOrDefault<string>();
+        Assert.Equal("US Dollar, Australian Dollar, Chinese Yuan, Hong Kong Dollar, Israeli Shekel, South Korean Won, Russian Ruble", result);
+    }
+
+    [Fact]
+    public void TextJoin_Range2D_CommaSpace_IgnoreEmptyVariants()
+    {
+        var sheet = new Sheet(20, 10);
+        // A2:B8 grid
+        sheet.Cells["A2"].Value = "a1";
+        sheet.Cells["B2"].Value = "b1";
+        sheet.Cells["A3"].Value = "a2";
+        sheet.Cells["B3"].Value = "b2";
+        sheet.Cells["A4"].Value = string.Empty; // empty cell value
+        sheet.Cells["B4"].Value = string.Empty;
+        sheet.Cells["A5"].Value = "a5";
+        sheet.Cells["B5"].Value = "b5";
+        sheet.Cells["A6"].Value = "a6";
+        sheet.Cells["B6"].Value = "b6";
+        sheet.Cells["A7"].Value = "a7";
+        sheet.Cells["B7"].Value = "b7";
+        sheet.Cells["B1"].Formula = "=TEXTJOIN(\", \", TRUE, A2:B7)";
+        Assert.Equal("a1, b1, a2, b2, a5, b5, a6, b6, a7, b7", sheet.Cells["B1"].Data.Value);
+
+        sheet.Cells["C1"].Formula = "=TEXTJOIN(\", \", FALSE, A2:B7)";
+        Assert.Equal("a1, b1, a2, b2, , , a5, b5, a6, b6, a7, b7", sheet.Cells["C1"].Data.Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/TodayFunctionTests.cs

@@ -0,0 +1,26 @@
+using Xunit;
+using Radzen.Blazor.Spreadsheet;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class TodayFunctionTests
+{
+    [Fact]
+    public void Today_ReturnsCurrentDate()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=TODAY()";
+        var dt = sheet.Cells["A1"].Data.GetValueOrDefault<System.DateTime>();
+        Assert.Equal(System.DateTime.Today.Date, dt.Date);
+    }
+
+    [Fact]
+    public void Today_PlusFiveDays()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=TODAY()+5";
+        var serial = sheet.Cells["A1"].Data.GetValueOrDefault<double>();
+        var expected = System.DateTime.Today.AddDays(5).ToNumber();
+        Assert.Equal(expected, serial);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/TrimFunctionTests.cs

@@ -0,0 +1,31 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class TrimFunctionTests
+{
+    [Fact]
+    public void Trim_RemovesLeadingTrailingAndCollapsesInternalSpaces()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=TRIM(\" First  Quarter   Earnings \")";
+        Assert.Equal("First Quarter Earnings", sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Trim_Empty_ReturnsEmpty()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=TRIM(\"   \")";
+        Assert.Equal(string.Empty, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Trim_TextCell_Works()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["B1"].Value = "  Hello   world  ";
+        sheet.Cells["A1"].Formula = "=TRIM(B1)";
+        Assert.Equal("Hello world", sheet.Cells["A1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/TruncFunctionTests.cs

@@ -0,0 +1,31 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class TruncFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldTruncatePositive()
+    {
+        sheet.Cells["A1"].Formula = "=TRUNC(8.9)";
+        Assert.Equal(8d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldTruncateNegative()
+    {
+        sheet.Cells["A1"].Formula = "=TRUNC(0-8.9)";
+        Assert.Equal(-8d, sheet.Cells["A1"].Value);
+    }
+
+    [Fact]
+    public void ShouldTruncateLessThanOne()
+    {
+        sheet.Cells["A1"].Formula = "=TRUNC(0.45)";
+        Assert.Equal(0d, sheet.Cells["A1"].Value);
+    }
+}
+
+

Radzen.Blazor.Tests/Spreadsheet/UpperFunctionTests.cs

@@ -0,0 +1,24 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class UpperFunctionTests
+{
+    [Fact]
+    public void Upper_ConvertsToUppercase()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A2"].Value = "total";
+        sheet.Cells["B1"].Formula = "=UPPER(A2)";
+        Assert.Equal("TOTAL", sheet.Cells["B1"].Data.Value);
+    }
+
+    [Fact]
+    public void Upper_AlreadyUppercase()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A3"].Value = "Yield";
+        sheet.Cells["B1"].Formula = "=UPPER(A3)";
+        Assert.Equal("YIELD", sheet.Cells["B1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/ValueFunctionTests.cs

@@ -0,0 +1,22 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class ValueFunctionTests
+{
+    [Fact]
+    public void Value_ParsesCurrency()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=VALUE(\"$1,000\")";
+        Assert.Equal(1000d, sheet.Cells["A1"].Data.Value);
+    }
+
+    [Fact]
+    public void Value_TimeDifferenceFractionOfDay()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=VALUE(\"16:48:00\")-VALUE(\"12:00:00\")";
+        Assert.Equal(0.2d, sheet.Cells["A1"].Data.Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/VerticalLookupFunctionTests.cs

@@ -0,0 +1,61 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class VerticalLookupFunctionTests
+{
+    readonly Sheet sheet = new(10, 10);
+
+    [Fact]
+    public void ShouldFindExactMatchInTwoColumnRange()
+    {
+        sheet.Cells["A1"].Value = "T-Shirt";
+        sheet.Cells["A2"].Value = "Jeans";
+        sheet.Cells["B1"].Value = 19.99;
+        sheet.Cells["B2"].Value = 29.99;
+
+        sheet.Cells["C1"].Formula = "=VLOOKUP(\"T-Shirt\",A1:B2,2,0)";
+
+        Assert.Equal(19.99, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnNAWhenNoExactMatch()
+    {
+        sheet.Cells["A1"].Value = "Hat";
+        sheet.Cells["B1"].Value = 9.99;
+
+        sheet.Cells["C1"].Formula = "=VLOOKUP(\"Gloves\",A1:B1,2,0)";
+
+        Assert.Equal(CellError.NA, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldFindApproximateMatchInSortedFirstColumn()
+    {
+        // First column sorted ascending
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+
+        sheet.Cells["B1"].Value = "Low";
+        sheet.Cells["B2"].Value = "Medium";
+        sheet.Cells["B3"].Value = "High";
+
+        // search_key 25 -> should pick row with 20
+        sheet.Cells["C1"].Formula = "=VLOOKUP(25,A1:B3,2,1)";
+
+        Assert.Equal("Medium", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldErrorWhenIndexOutOfRange()
+    {
+        sheet.Cells["A1"].Value = "X";
+        sheet.Cells["B1"].Value = 1;
+
+        sheet.Cells["C1"].Formula = "=VLOOKUP(\"X\",A1:B1,3,0)";
+
+        Assert.Equal(CellError.Ref, sheet.Cells["C1"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/WeekdayFunctionTests.cs

@@ -0,0 +1,42 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class WeekdayFunctionTests
+{
+    [Fact]
+    public void Weekday_Default_SundayToSaturday()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2008, 2, 14)); // Thursday
+        sheet.Cells["B1"].Formula = "=WEEKDAY(A1)"; // default 1: Sun=1..Sat=7
+        Assert.Equal(5, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Weekday_Type2_MondayToSunday()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2008, 2, 14)); // Thursday
+        sheet.Cells["B1"].Formula = "=WEEKDAY(A1, 2)"; // Mon=1..Sun=7
+        Assert.Equal(4, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Weekday_Type3_MondayZero_SundaySix()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2008, 2, 14)); // Thursday
+        sheet.Cells["B1"].Formula = "=WEEKDAY(A1, 3)"; // Mon=0..Sun=6
+        Assert.Equal(3, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Weekday_InvalidReturnType_ReturnsNumError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2008, 2, 14));
+        sheet.Cells["B1"].Formula = "=WEEKDAY(A1, 10)"; // invalid
+        Assert.Equal(CellError.Num, sheet.Cells["B1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/WeeknumFunctionTests.cs

@@ -0,0 +1,42 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class WeeknumFunctionTests
+{
+    [Fact]
+    public void Weeknum_Default_SundayStart()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2012, 3, 9)); // Excel example
+        sheet.Cells["B1"].Formula = "=WEEKNUM(A1)"; // default 1
+        Assert.Equal(10, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Weeknum_Type2_MondayStart()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2012, 3, 9));
+        sheet.Cells["B1"].Formula = "=WEEKNUM(A1, 2)"; // Monday start, System 1
+        Assert.Equal(11, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Weeknum_Type21_ISO()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2012, 3, 9));
+        sheet.Cells["B1"].Formula = "=WEEKNUM(A1, 21)"; // ISO
+        Assert.Equal(10, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Weeknum_InvalidReturnType_ReturnsNumError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2012, 3, 9));
+        sheet.Cells["B1"].Formula = "=WEEKNUM(A1, 4)"; // invalid code
+        Assert.Equal(CellError.Num, sheet.Cells["B1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/XLookupFunctionTests.cs

@@ -0,0 +1,114 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class XLookupFunctionTests
+{
+    readonly Sheet sheet = new(20, 10);
+
+    [Fact]
+    public void ShouldFindExactMatchAndReturnFromAnotherColumn()
+    {
+        sheet.Cells["A1"].Value = "P1";
+        sheet.Cells["A2"].Value = "P2";
+        sheet.Cells["B1"].Value = 10;
+        sheet.Cells["B2"].Value = 20;
+
+        sheet.Cells["C1"].Formula = "=XLOOKUP(\"P2\",A1:A2,B1:B2)";
+
+        Assert.Equal(20d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnIfNotFoundValue()
+    {
+        sheet.Cells["A1"].Value = "P1";
+        sheet.Cells["B1"].Value = 10;
+
+        sheet.Cells["C1"].Formula = "=XLOOKUP(\"P2\",A1:A1,B1:B1,\"Missing\")";
+
+        Assert.Equal("Missing", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldSupportWildcardMatch()
+    {
+        sheet.Cells["A1"].Value = "Item-100";
+        sheet.Cells["A2"].Value = "Item-200";
+        sheet.Cells["B1"].Value = "A";
+        sheet.Cells["B2"].Value = "B";
+
+        sheet.Cells["C1"].Formula = "=XLOOKUP(\"Item-2*\",A1:A2,B1:B2,\"\",2)";
+
+        Assert.Equal("B", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldFindNextSmallerWhenNotFound()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+        sheet.Cells["B1"].Value = "L";
+        sheet.Cells["B2"].Value = "M";
+        sheet.Cells["B3"].Value = "H";
+
+        sheet.Cells["C1"].Formula = "=XLOOKUP(25,A1:A3,B1:B3,\"\",0-1)";
+
+        Assert.Equal("M", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldFindNextLargerWhenNotFound()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+        sheet.Cells["B1"].Value = "L";
+        sheet.Cells["B2"].Value = "M";
+        sheet.Cells["B3"].Value = "H";
+
+        sheet.Cells["C1"].Formula = "=XLOOKUP(25,A1:A3,B1:B3,\"\",1)";
+
+        Assert.Equal("H", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldSupportReverseSearch()
+    {
+        sheet.Cells["A1"].Value = "A";
+        sheet.Cells["A2"].Value = "A";
+        sheet.Cells["B1"].Value = 1;
+        sheet.Cells["B2"].Value = 2;
+
+        sheet.Cells["C1"].Formula = "=XLOOKUP(\"A\",A1:A2,B1:B2,\"\",0,0-1)";
+
+        Assert.Equal(2d, sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldSupportBinarySearchAscending()
+    {
+        sheet.Cells["A1"].Value = 10;
+        sheet.Cells["A2"].Value = 20;
+        sheet.Cells["A3"].Value = 30;
+        sheet.Cells["B1"].Value = "L";
+        sheet.Cells["B2"].Value = "M";
+        sheet.Cells["B3"].Value = "H";
+
+        sheet.Cells["C1"].Formula = "=XLOOKUP(20,A1:A3,B1:B3,\"\",0,2)";
+
+        Assert.Equal("M", sheet.Cells["C1"].Value);
+    }
+
+    [Fact]
+    public void ShouldReturnNAWhenNotFoundAndNoIfNotFound()
+    {
+        sheet.Cells["A1"].Value = "A";
+        sheet.Cells["B1"].Value = 1;
+
+        sheet.Cells["C1"].Formula = "=XLOOKUP(\"B\",A1:A1,B1:B1)";
+
+        Assert.Equal(CellError.NA, sheet.Cells["C1"].Value);
+    }
+}

Radzen.Blazor.Tests/Spreadsheet/YearFunctionTests.cs

@@ -0,0 +1,31 @@
+using Xunit;
+
+namespace Radzen.Blazor.Spreadsheet.Tests;
+
+public class YearFunctionTests
+{
+    [Fact]
+    public void Year_FromDateSerial_ReturnsYear()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=YEAR(VALUE(\"2025-05-23\"))";
+        Assert.Equal(2025, sheet.Cells["A1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Year_FromDateValue_ReturnsYear()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Data = CellData.FromDate(new System.DateTime(2023, 7, 5));
+        sheet.Cells["B1"].Formula = "=YEAR(A1)";
+        Assert.Equal(2023, sheet.Cells["B1"].Data.GetValueOrDefault<double>());
+    }
+
+    [Fact]
+    public void Year_InvalidText_ReturnsValueError()
+    {
+        var sheet = new Sheet(10, 10);
+        sheet.Cells["A1"].Formula = "=YEAR(\"abc\")";
+        Assert.Equal(CellError.Value, sheet.Cells["A1"].Data.GetValueOrDefault<CellError>());
+    }
+}

Radzen.Blazor/DropDownBase.cs

@@ -508,7 +508,7 @@ namespace Radzen
         /// <param name="item">The item.</param>
         /// <param name="property">The property.</param>
         /// <returns>System.Object.</returns>
-        public virtual object? GetItemOrValueFromProperty(object? item, string property)
+        public object? GetItemOrValueFromProperty(object? item, string property)
         {
             if (item != null)
             {
@@ -651,11 +651,7 @@ namespace Radzen
         /// <param name="shouldSelectOnChange">Should select item on item change with keyboard.</param>
         protected virtual async Task HandleKeyPress(Microsoft.AspNetCore.Components.Web.KeyboardEventArgs args, bool isFilter = false, bool? shouldSelectOnChange = null)
         {
-            ArgumentNullException.ThrowIfNull(args);
-
-            var key = args.Code != null ? args.Code : args.Key;
-
-            if (Disabled || Data == null || args == null || key == null)
+            if (Disabled || Data == null || args == null)
                 return;
 
             List<object> items = Enumerable.Empty<object>().ToList();
@@ -679,6 +675,8 @@ namespace Radzen
                 }
             }
 
+            var key = args.Code != null ? args.Code : args.Key;
+
             if (!args.AltKey && (key == "ArrowDown" || key == "ArrowLeft" || key == "ArrowUp" || key == "ArrowRight"))
             {
                 preventKeydown = true;
@@ -938,25 +936,6 @@ namespace Radzen
             }
         }
 
-        /// <summary>
-        /// Handles filter input changes (e.g. paste).
-        /// </summary>
-        /// <param name="args">The <see cref="ChangeEventArgs"/> instance containing the event data.</param>
-        protected virtual async Task OnFilterInput(ChangeEventArgs args)
-        {
-            ArgumentNullException.ThrowIfNull(args);
-
-            searchText = $"{args.Value}"; 
-            await SearchTextChanged.InvokeAsync(searchText);
-
-            if (ResetSelectedIndexOnFilter)
-            {
-                selectedIndex = -1;
-            }
-
-            Debounce(DebounceFilter, FilterDelay);
-        }
-
         /// <summary>
         /// Gets the load data arguments.
         /// </summary>

Radzen.Blazor/GroupRowRenderEventArgs.cs

@@ -17,12 +17,6 @@ public class GroupRowRenderEventArgs
     /// </summary>
     public Group? Group { get; internal set; }
 
-    /// <summary>
-    /// Gets or sets a value indicating whether this group row is expandable.
-    /// </summary>
-    /// <value><c>true</c> if expandable; otherwise, <c>false</c>.</value>
-    public bool Expandable { get; set; }
-
     /// <summary>
     /// Gets or sets a value indicating whether this group row is expanded.
     /// </summary>

Radzen.Blazor/IRadzenSpiderChart.cs

@@ -1,22 +0,0 @@
-using System.Threading.Tasks;
-
-namespace Radzen.Blazor
-{
-    /// <summary>
-    /// Non-generic contract for <see cref="RadzenSpiderChart"/> used by configuration components
-    /// like <see cref="RadzenSpiderLegend"/> without relying on reflection (important for trimming/AOT).
-    /// </summary>
-    public interface IRadzenSpiderChart
-    {
-        /// <summary>
-        /// Gets or sets the legend configuration for the chart.
-        /// </summary>
-        RadzenSpiderLegend Legend { get; set; }
-
-        /// <summary>
-        /// Requests the chart to refresh its rendering.
-        /// </summary>
-        Task Refresh();
-    }
-}
-

Radzen.Blazor/IRadzenSpiderSeries.cs

@@ -1,29 +0,0 @@
-using Microsoft.AspNetCore.Components;
-using System.Collections.Generic;
-
-namespace Radzen.Blazor
-{
-    /// <summary>
-    /// Non-generic contract for spider series so <see cref="RadzenSpiderChart"/> can be non-generic.
-    /// </summary>
-    internal interface IRadzenSpiderSeries
-    {
-        int Index { get; set; }
-        string Title { get; }
-        bool IsVisible { get; set; }
-        bool MarkersVisible { get; }
-        double MarkerSize { get; }
-        double StrokeWidth { get; }
-
-        IEnumerable<string> GetCategories();
-        IEnumerable<double> GetValues();
-        double GetValue(string category);
-        object? GetData(string category);
-        string FormatValue(double value);
-
-        double MeasureLegend();
-        RenderFragment RenderLegendItem();
-        void ForceUpdate();
-    }
-}
-

Radzen.Blazor/PropertyAccess.cs

@@ -26,79 +26,61 @@ public static class PropertyAccess
 
         if (propertyName.Contains('[', StringComparison.Ordinal))
         {
-            var arg0 = Expression.Parameter(typeof(TItem), "x");
-            return Expression.Lambda<Func<TItem, TValue>>(
-                QueryableExtension.GetNestedPropertyExpression(arg0, propertyName, type),
-                arg0
-            ).Compile();
+            var arg = Expression.Parameter(typeof(TItem));
+
+            return Expression.Lambda<Func<TItem, TValue>>(QueryableExtension.GetNestedPropertyExpression(arg, propertyName ?? string.Empty, type), arg).Compile();
         }
-
-        var arg = Expression.Parameter(typeof(TItem), "x");
-        Expression body = arg;
-
-        if (type != null)
-            body = Expression.Convert(body, type);
-
-        Expression AccessNoInterface(Expression instance, string memberName)
+        else
         {
-            if (instance.Type.IsInterface)
+            var arg = Expression.Parameter(typeof(TItem));
+
+            Expression body = arg;
+
+            if (type != null)
             {
-                var declaringType =
-                    new[] { instance.Type }
-                        .Concat(instance.Type.GetInterfaces())
-                        .FirstOrDefault(t => t.GetProperty(memberName) != null);
-
-                if (declaringType == null)
-                    throw new InvalidOperationException($"Member '{memberName}' not found on interface '{instance.Type}'.");
-
-                return Expression.Property(instance, declaringType, memberName);
+                body = Expression.Convert(body, type);
             }
 
-            try
+            foreach (var member in propertyName.Split("."))
             {
-                return Expression.PropertyOrField(instance, memberName);
-            }
-            catch (AmbiguousMatchException)
-            {
-                var prop = instance.Type.GetProperty(memberName,
-                    BindingFlags.Instance | BindingFlags.Public | BindingFlags.FlattenHierarchy);
-                if (prop != null) return Expression.Property(instance, prop);
+                if (body.Type.IsInterface)
+                {
+                    body = Expression.Property(body,
+                        new[] { body.Type }.Concat(body.Type.GetInterfaces()).FirstOrDefault(t => t.GetProperty(member) != null)!,
+                        member
+                    );
+                }
+                else
+                {
+                    try
+                    {
+                        body = Expression.PropertyOrField(body, member);
+                    }
+                    catch (AmbiguousMatchException)
+                    {
+                        var property = body.Type.GetProperty(member, BindingFlags.Instance | BindingFlags.Public | BindingFlags.FlattenHierarchy);
 
-                var field = instance.Type.GetField(memberName,
-                    BindingFlags.Instance | BindingFlags.Public | BindingFlags.FlattenHierarchy);
-                if (field != null) return Expression.Field(instance, field);
+                        if (property != null)
+                        {
+                            body = Expression.Property(body, property);
+                        }
+                        else
+                        {
+                            var field = body.Type.GetField(member, BindingFlags.Instance | BindingFlags.Public | BindingFlags.FlattenHierarchy);
 
-                throw;
+                            if (field != null)
+                            {
+                                body = Expression.Field(body, field);
+                            }
+                        }
+                    }
+                }
             }
+
+            body = Expression.Convert(body, typeof(TValue));
+
+            return Expression.Lambda<Func<TItem, TValue>>(body, arg).Compile();
         }
-
-        Expression AccessWithNullPropagation(Expression instance, string memberName)
-        {
-            var underlying = Nullable.GetUnderlyingType(instance.Type);
-            if (underlying != null && memberName is not ("Value" or "HasValue"))
-            {
-                var hasValue = Expression.Property(instance, "HasValue");
-                var value = Expression.Property(instance, "Value");
-
-                var accessed = AccessNoInterface(value, memberName);
-                return Expression.Condition(hasValue, accessed, Expression.Default(accessed.Type));
-            }
-
-            if (!instance.Type.IsValueType)
-            {
-                var notNull = Expression.NotEqual(instance, Expression.Constant(null, instance.Type));
-                var accessed = AccessNoInterface(instance, memberName);
-                return Expression.Condition(notNull, accessed, Expression.Default(accessed.Type));
-            }
-
-            return AccessNoInterface(instance, memberName);
-        }
-
-        foreach (var member in propertyName.Split('.'))
-            body = AccessWithNullPropagation(body, member);
-
-        body = Expression.Convert(body, typeof(TValue));
-        return Expression.Lambda<Func<TItem, TValue>>(body, arg).Compile();
     }
 
     /// <summary>
@@ -420,7 +402,7 @@ public static class PropertyAccess
         if (type != null)
         {
             return !type.IsInterface ?
-                (Nullable.GetUnderlyingType(type) ?? type).GetProperty(property ?? "")?.PropertyType :
+                type.GetProperty(property ?? "")?.PropertyType :
                     new Type[] { type }
                     .Concat(type.GetInterfaces())
                     .FirstOrDefault(t => t.GetProperty(property ?? "") != null)?

Radzen.Blazor/QueryableExtension.cs

@@ -41,65 +41,6 @@ namespace Radzen
             return source.Provider.CreateQuery(selectExpression);
         }
 
-        /// <summary>
-        /// Projects each element of a sequence into a collection of property values.
-        /// </summary>
-        public static IQueryable Select(this IQueryable source, IEnumerable<string> propertyNames)
-        {
-            ArgumentNullException.ThrowIfNull(source);
-            ArgumentNullException.ThrowIfNull(propertyNames);
-
-            var parameter = Expression.Parameter(source.ElementType, "x");
-
-            var bindings = new List<MemberBinding>();
-            var allProperties = source.ElementType.GetProperties();
-
-            foreach (var property in allProperties.Where(p => propertyNames.Contains(p.Name)))
-            {
-                bindings.Add(Expression.Bind(property, Expression.Property(parameter, property)));
-            }
-
-            var body = Expression.MemberInit(Expression.New(source.ElementType), bindings);
-
-            var delegateType = typeof(Func<,>).MakeGenericType(source.ElementType, source.ElementType);
-
-            var lambda = Expression.Lambda(delegateType, body, parameter);
-
-            var selectExpression = Expression.Call(typeof(Queryable),
-                nameof(Queryable.Select), [source.ElementType, source.ElementType], source.Expression,
-                    Expression.Quote(lambda));
-
-            return source.Provider.CreateQuery(selectExpression);
-        }
-
-        /// <summary>
-        /// Projects each element of a sequence into a collection of property values.
-        /// </summary>
-        public static IQueryable<T> Select<T>(this IQueryable<T> source, IEnumerable<string> propertyNames)
-        {
-            ArgumentNullException.ThrowIfNull(source);
-            ArgumentNullException.ThrowIfNull(propertyNames);
-
-            var parameter = Expression.Parameter(typeof(T), "x");
-
-            var bindings = new List<MemberBinding>();
-            var allProperties = typeof(T).GetProperties();
-
-            foreach (var property in allProperties.Where(p => propertyNames.Contains(p.Name)))
-            {
-                bindings.Add(Expression.Bind(property, Expression.Property(parameter, property)));
-            }
-
-            var body = Expression.MemberInit(Expression.New(typeof(T)), bindings);
-
-            var lambda = Expression.Lambda<Func<T, T>>(body, parameter);
-
-            var selectExpression = Expression.Call(typeof(Queryable),
-                nameof(Queryable.Select), [typeof(T), typeof(T)], source.Expression,
-                    Expression.Quote(lambda));
-
-            return source.Provider.CreateQuery<T>(selectExpression);
-        }
 
         /// <summary>
         /// Projects each element of a sequence to an IEnumerable and flattens the resulting sequences into one sequence.
@@ -478,150 +419,79 @@ namespace Radzen
 
         internal static Expression GetNestedPropertyExpression(Expression expression, string property, Type? type = null)
         {
-            ArgumentNullException.ThrowIfNull(expression);
-            if (string.IsNullOrWhiteSpace(property)) return Expression.Constant(null, typeof(object));
-
             var parts = property.Split(separator, 2);
-            var currentPart = parts[0];
-
-            static Expression BuildIsNull(Expression expr)
-            {
-                var underlying = Nullable.GetUnderlyingType(expr.Type);
-                if (underlying != null)
-                {
-                    return Expression.Not(Expression.Property(expr, "HasValue"));
-                }
-
-                if (!expr.Type.IsValueType)
-                {
-                    return Expression.Equal(expr, Expression.Constant(null, expr.Type));
-                }
-
-                return Expression.Constant(false);
-            }
-
-            static Expression UnwrapNullableIfNeeded(Expression expr)
-            {
-                return Nullable.GetUnderlyingType(expr.Type) != null
-                    ? Expression.Property(expr, "Value")
-                    : expr;
-            }
-
-            static Expression AccessMember(Expression instance, string memberName)
-            {
-                var t = instance.Type;
-
-                if (t.IsInterface)
-                {
-                    var declaring =
-                        new[] { t }.Concat(t.GetInterfaces())
-                            .FirstOrDefault(i => i.GetProperty(memberName) != null);
-
-                    if (declaring == null)
-                        throw new InvalidOperationException($"Member '{memberName}' not found on interface '{t}'.");
-
-                    return Expression.Property(instance, declaring, memberName);
-                }
-
-                try
-                {
-                    return Expression.PropertyOrField(instance, memberName);
-                }
-                catch (AmbiguousMatchException)
-                {
-                    var prop = t.GetProperty(memberName, BindingFlags.Instance | BindingFlags.Public | BindingFlags.FlattenHierarchy);
-                    if (prop != null) return Expression.Property(instance, prop);
-
-                    var field = t.GetField(memberName, BindingFlags.Instance | BindingFlags.Public | BindingFlags.FlattenHierarchy);
-                    if (field != null) return Expression.Field(instance, field);
-
-                    throw;
-                }
-            }
-
-            static Expression NullPropagate(Expression parent, Expression accessed)
-            {
-                var isNull = BuildIsNull(parent);
-
-                var whenNull = Expression.Default(accessed.Type);
-
-                return Expression.Condition(isNull, whenNull, accessed);
-            }
-
+            string currentPart = parts[0];
             Expression member;
 
-            var parentForAccess = UnwrapNullableIfNeeded(expression);
-
-            if ((parentForAccess.Type.IsGenericType && typeof(IDictionary<,>).IsAssignableFrom(parentForAccess.Type.GetGenericTypeDefinition())) ||
-                typeof(IDictionary).IsAssignableFrom(parentForAccess.Type) ||
-                typeof(System.Data.DataRow).IsAssignableFrom(parentForAccess.Type))
+            if (expression.Type.IsGenericType && typeof(IDictionary<,>).IsAssignableFrom(expression.Type.GetGenericTypeDefinition()) ||
+                typeof(IDictionary).IsAssignableFrom(expression.Type) || typeof(System.Data.DataRow).IsAssignableFrom(expression.Type))
             {
                 var key = currentPart.Split('"')[1];
                 var typeString = currentPart.Split('(')[0];
 
-                var indexer =
-                    typeof(System.Data.DataRow).IsAssignableFrom(parentForAccess.Type)
-                        ? Expression.Property(parentForAccess, parentForAccess.Type.GetProperty("Item", new[] { typeof(string) })!, Expression.Constant(key))
-                        : Expression.Property(parentForAccess, parentForAccess.Type.GetProperty("Item")!, Expression.Constant(key));
-
-                var targetType =
-                    parts.Length > 1
-                        ? indexer.Type
-                        : type
-                            ?? Type.GetType(
-                                typeString.EndsWith('?')
-                                    ? $"System.Nullable`1[System.{typeString.TrimEnd('?')}]"
-                                    : $"System.{typeString}"
-                            )
-                            ?? typeof(object);
-
-                member = Expression.Convert(indexer, targetType);
-
-                member = NullPropagate(expression, member);
+                var indexer = typeof(System.Data.DataRow).IsAssignableFrom(expression.Type) ?
+                    Expression.Property(expression, expression.Type.GetProperty("Item", new[] { typeof(string) })!, Expression.Constant(key)) :
+                        Expression.Property(expression, expression.Type.GetProperty("Item")!, Expression.Constant(key));
+                member = Expression.Convert(
+                    indexer,
+                    parts.Length > 1 ? indexer.Type : type ?? Type.GetType(typeString.EndsWith('?') ? $"System.Nullable`1[System.{typeString.TrimEnd('?')}]" : $"System.{typeString}") ?? typeof(object));
             }
-
-            else if (currentPart.Contains('[', StringComparison.Ordinal))
+            else if (currentPart.Contains('[', StringComparison.Ordinal)) // Handle array or list indexing
             {
                 var indexStart = currentPart.IndexOf('[', StringComparison.Ordinal);
                 var propertyName = currentPart.Substring(0, indexStart);
                 var indexString = currentPart.Substring(indexStart + 1, currentPart.Length - indexStart - 2);
 
-                var collection = AccessMember(parentForAccess, propertyName);
-                collection = NullPropagate(expression, collection);
-
-                if (!int.TryParse(indexString, out var index))
-                    throw new ArgumentException($"Invalid index format: {indexString}");
-
-                var underlyingCollection = Nullable.GetUnderlyingType(collection.Type) != null
-                    ? Expression.Property(collection, "Value")
-                    : collection;
-
-                Expression indexed;
-                if (underlyingCollection.Type.IsArray)
+                member = Expression.PropertyOrField(expression, propertyName);
+                if (int.TryParse(indexString, out int index))
                 {
-                    indexed = Expression.ArrayIndex(underlyingCollection, Expression.Constant(index));
+                    if (member.Type.IsArray)
+                    {
+                        member = Expression.ArrayIndex(member, Expression.Constant(index));
+                    }
+                    else if (member.Type.IsGenericType &&
+                             (member.Type.GetGenericTypeDefinition() == typeof(List<>) ||
+                              typeof(IList<>).IsAssignableFrom(member.Type.GetGenericTypeDefinition())))
+                    {
+                        var itemProperty = member.Type.GetProperty("Item");
+                        if (itemProperty != null)
+                        {
+                            member = Expression.Property(member, itemProperty, Expression.Constant(index));
+                        }
+                    }
                 }
                 else
                 {
-                    var itemProp = underlyingCollection.Type.GetProperty("Item");
-                    if (itemProp == null)
-                        throw new InvalidOperationException($"Type '{underlyingCollection.Type}' has no indexer 'Item'.");
-
-                    indexed = Expression.Property(underlyingCollection, itemProp, Expression.Constant(index));
+                    throw new ArgumentException($"Invalid index format: {indexString}");
                 }
-
-                member = NullPropagate(collection, indexed);
+            }
+            else if (expression != null && expression.Type != null && expression.Type.IsInterface)
+            {
+                member = Expression.Property(expression,
+                    new[] { expression.Type }.Concat(expression.Type.GetInterfaces()).FirstOrDefault(t => t.GetProperty(currentPart) != null)!,
+                    currentPart
+                );
             }
             else
             {
-                var accessed = AccessMember(parentForAccess, currentPart);
-                member = NullPropagate(expression, accessed);
+            if (expression == null || string.IsNullOrEmpty(currentPart))
+            {
+                return Expression.Constant(null, typeof(object));
             }
 
-            if (parts.Length > 1)
-                return GetNestedPropertyExpression(member, parts[1], type);
+            var p = expression.Type?.GetProperty(currentPart, BindingFlags.Public | BindingFlags.Instance);
+            member = p != null ? Expression.Property(expression, p) : Expression.PropertyOrField(expression, currentPart);
+            }
 
-            return member;
+            if (expression != null && expression.Type != null && expression.Type.IsValueType && Nullable.GetUnderlyingType(expression.Type) == null)
+            {
+                expression = Expression.Convert(expression, typeof(object));
+            }
+
+            return parts.Length > 1 ? GetNestedPropertyExpression(member, parts[1], type) :
+                (Nullable.GetUnderlyingType(member.Type) != null || member.Type == typeof(string)) ?
+                    expression != null ? Expression.Condition(Expression.Equal(expression, Expression.Constant(null)), Expression.Constant(null, member.Type), member) : member :
+                    member;
         }
 
         internal static Expression GetExpression<T>(ParameterExpression parameter, FilterDescriptor filter, FilterCaseSensitivity filterCaseSensitivity, Type type)
@@ -1825,7 +1695,7 @@ namespace Radzen
             return columns
                 .Where(c => c.Filterable
                     && c.FilterPropertyType != null
-                    && (!(c.GetFilterValue() == null || (c.GetFilterValue() as string)?.Length == 0)
+                    && (!string.IsNullOrEmpty(c.GetFilterValue() as string)
                         || !c.CanSetFilterValue()
                         || c.HasCustomFilter())
                     && c.GetFilterProperty() != null)

Radzen.Blazor/Radzen.Blazor.csproj

@@ -11,7 +11,7 @@
     <IsPackable>true</IsPackable>
     <PackageId>Radzen.Blazor</PackageId>
     <Product>Radzen.Blazor</Product>
-    <Version>8.7.5</Version>
+    <Version>8.6.3</Version>
     <Copyright>Radzen Ltd.</Copyright>
     <Authors>Radzen Ltd.</Authors>
     <Description>Radzen Blazor is the most sophisticated free UI component library for Blazor, featuring 100+ native components including DataGrid, Scheduler, Charts, and advanced theming with full support for Material Design and Fluent UI.</Description>

Radzen.Blazor/RadzenBarcode.razor.cs

@@ -1,11 +1,9 @@
 using Microsoft.AspNetCore.Components;
-using Microsoft.JSInterop;
 using System;
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
 using System.Text;
-using System.Threading.Tasks;
 
 namespace Radzen.Blazor
 {
@@ -95,6 +93,22 @@ namespace Radzen.Blazor
             _ => false
         };
 
+        internal readonly struct BarcodeRect
+        {
+            public readonly double X;
+            public readonly double Y;
+            public readonly double Width;
+            public readonly double Height;
+
+            public BarcodeRect(double x, double y, double width, double height)
+            {
+                X = x;
+                Y = y;
+                Width = width;
+                Height = height;
+            }
+        }
+
         /// <summary>
         /// Gets or sets the barcode value to encode.
         /// </summary>
@@ -261,20 +275,894 @@ namespace Radzen.Blazor
             if (vbWidth <= 0) vbWidth = 1;
             return (geometry.bars, vbWidth, checksumText, null);
         }
+    }
 
-        /// <summary>
-        /// Returns the SVG markup of the rendered QR code as a string.
-        /// </summary>
-        /// <returns>
-        /// A <see cref="Task{String}"/> representing the asynchronous operation. The task result contains the SVG markup of the QR code.
-        /// </returns>
-        public async Task<string> ToSvg()
+    internal static class RadzenBarcodeEncoder
+    {
+        // Code 128 patterns (0..106). Each entry is 6 digits (bar/space/bar/space/bar/space) module widths.
+        // Stop code (106) is 7 digits in the spec (includes a final bar). We keep it as 7 digits and handle it.
+        static readonly string[] Code128Patterns = new[]
         {
-            if (JSRuntime != null)
+            "212222","222122","222221","121223","121322","131222","122213","122312","132212","221213",
+            "221312","231212","112232","122132","122231","113222","123122","123221","223211","221132",
+            "221231","213212","223112","312131","311222","321122","321221","312212","322112","322211",
+            "212123","212321","232121","111323","131123","131321","112313","132113","132311","211313",
+            "231113","231311","112133","112331","132131","113123","113321","133121","313121","211331",
+            "231131","213113","213311","213131","311123","311321","331121","312113","312311","332111",
+            "314111","221411","431111","111224","111422","121124","121421","141122","141221","112214",
+            "112412","122114","122411","142112","142211","241211","221114","413111","241112","134111",
+            "111242","121142","121241","114212","124112","124211","411212","421112","421211","212141",
+            "214121","412121","111143","111341","131141","114113","114311","411113","411311","113141",
+            "114131","311141","411131","211412","211214","211232","2331112"
+        };
+
+        public static IReadOnlyList<int> EncodeCode128B(string value) => EncodeCode128B(value, out _);
+
+        public static IReadOnlyList<int> EncodeCode128B(string value, out int checksum)
+        {
+            // Code 128 subset B supports ASCII 32..127 (inclusive). We treat 127 as DEL.
+            var codes = new List<int>(value.Length + 3);
+            const int startB = 104;
+            const int stop = 106;
+
+            codes.Add(startB);
+
+            for (int i = 0; i < value.Length; i++)
             {
-                return await JSRuntime.InvokeAsync<string>("Radzen.outerHTML", Element);
+                var ch = value[i];
+                int ascii = ch;
+                if (ascii < 32 || ascii > 127)
+                {
+                    throw new ArgumentException($"Code128B supports ASCII 32..127. Invalid character: U+{ascii:X4}.");
+                }
+
+                // In Code128B, code value is ascii - 32
+                codes.Add(ascii - 32);
             }
-            return string.Empty;
+
+            int checksumValue = codes[0];
+            for (int i = 1; i < codes.Count; i++)
+            {
+                checksumValue += codes[i] * i;
+            }
+            checksumValue %= 103;
+
+            // expose checksum (0..102)
+            checksum = checksumValue;
+
+            codes.Add(checksumValue);
+            codes.Add(stop);
+
+            // Convert codes to module pattern widths, alternating bar/space.
+            // Most codes are 6 digits; stop is 7 digits.
+            var modules = new List<int>(codes.Count * 6);
+            foreach (var code in codes)
+            {
+                var p = Code128Patterns[code];
+                for (int i = 0; i < p.Length; i++)
+                {
+                    modules.Add(p[i] - '0');
+                }
+            }
+
+            // Code 128 requires a 2-module termination bar after the stop pattern.
+            // Many pattern tables omit it because it can be represented by extending the
+            // final bar of the stop pattern by 2 modules.
+            if (modules.Count > 0)
+            {
+                modules[^1] += 2;
+            }
+
+            return modules;
+        }
+
+        static readonly Dictionary<char, string> Code39Map = new Dictionary<char, string>()
+        {
+            // Each pattern is 9 elements (bar/space alternating, starting with bar).
+            // 'n' = narrow (1), 'w' = wide (2). We expand to digits.
+            ['0'] = "nnnwwnwnn",
+            ['1'] = "wnnwnnnnw",
+            ['2'] = "nnwwnnnnw",
+            ['3'] = "wnwwnnnnn",
+            ['4'] = "nnnwwnnnw",
+            ['5'] = "wnnwwnnnn",
+            ['6'] = "nnwwwnnnn",
+            ['7'] = "nnnwnnwnw",
+            ['8'] = "wnnwnnwnn",
+            ['9'] = "nnwwnnwnn",
+            ['A'] = "wnnnnwnnw",
+            ['B'] = "nnwnnwnnw",
+            ['C'] = "wnwnnwnnn",
+            ['D'] = "nnnnwwnnw",
+            ['E'] = "wnnnwwnnn",
+            ['F'] = "nnwnwwnnn",
+            ['G'] = "nnnnnwwnw",
+            ['H'] = "wnnnnwwnn",
+            ['I'] = "nnwnnwwnn",
+            ['J'] = "nnnnwwwnn",
+            ['K'] = "wnnnnnnww",
+            ['L'] = "nnwnnnnww",
+            ['M'] = "wnwnnnnwn",
+            ['N'] = "nnnnwnnww",
+            ['O'] = "wnnnwnnwn",
+            ['P'] = "nnwnwnnwn",
+            ['Q'] = "nnnnnnwww",
+            ['R'] = "wnnnnnwwn",
+            ['S'] = "nnwnnnwwn",
+            ['T'] = "nnnnwnwwn",
+            ['U'] = "wwnnnnnnw",
+            ['V'] = "nwwnnnnnw",
+            ['W'] = "wwwnnnnnn",
+            ['X'] = "nwnnwnnnw",
+            ['Y'] = "wwnnwnnnn",
+            ['Z'] = "nwwnwnnnn",
+            ['-'] = "nwnnnnwnw",
+            ['.'] = "wwnnnnwnn",
+            [' '] = "nwwnnnwnn",
+            ['$'] = "nwnwnwnnn",
+            ['/'] = "nwnwnnnwn",
+            ['+'] = "nwnnnwnwn",
+            ['%'] = "nnnwnwnwn",
+            ['*'] = "nwnnwnwnn", // start/stop
+        };
+
+        public static IReadOnlyList<int> EncodeCode39(string value)
+        {
+            // Code39 traditionally uses uppercase
+            var text = value.ToUpperInvariant();
+
+            foreach (var ch in text)
+            {
+                if (!Code39Map.ContainsKey(ch))
+                {
+                    throw new ArgumentException($"Code39 does not support character '{ch}'.");
+                }
+            }
+
+            // Start + data + stop, inter-character gap (narrow space) between characters.
+            var full = "*" + text + "*";
+            var modules = new List<int>(full.Length * 10);
+
+            for (int idx = 0; idx < full.Length; idx++)
+            {
+                var pat = Code39Map[full[idx]];
+                for (int i = 0; i < pat.Length; i++)
+                {
+                    modules.Add(pat[i] == 'w' ? 2 : 1);
+                }
+
+                // Inter-character gap (narrow space) except after last char.
+                if (idx != full.Length - 1)
+                {
+                    modules.Add(1);
+                }
+            }
+
+            return modules;
+        }
+
+        public static IReadOnlyList<int> EncodeItf(string value)
+        {
+            var digits = new string(value.Where(char.IsDigit).ToArray());
+            if (digits.Length == 0)
+            {
+                throw new ArgumentException("ITF requires numeric input.");
+            }
+            if (digits.Length % 2 != 0)
+            {
+                // pad with leading zero (common behavior)
+                digits = "0" + digits;
+            }
+
+            const int narrow = 1;
+            const int wide = 3;
+
+            static string Pat(char d) => d switch
+            {
+                '0' => "nnwwn",
+                '1' => "wnnnw",
+                '2' => "nwnnw",
+                '3' => "wwnnn",
+                '4' => "nnwnw",
+                '5' => "wnwnn",
+                '6' => "nwwnn",
+                '7' => "nnnww",
+                '8' => "wnnwn",
+                '9' => "nwnwn",
+                _ => throw new ArgumentException("ITF requires numeric input.")
+            };
+
+            var widths = new List<int>(digits.Length * 10 + 16);
+
+            // Start: narrow bar, narrow space, narrow bar, narrow space  (1010)
+            widths.Add(narrow);
+            widths.Add(narrow);
+            widths.Add(narrow);
+            widths.Add(narrow);
+
+            for (int i = 0; i < digits.Length; i += 2)
+            {
+                var a = Pat(digits[i]);
+                var b = Pat(digits[i + 1]);
+
+                for (int j = 0; j < 5; j++)
+                {
+                    widths.Add(a[j] == 'w' ? wide : narrow); // bar
+                    widths.Add(b[j] == 'w' ? wide : narrow); // space
+                }
+            }
+
+            // Stop: wide bar, narrow space, narrow bar (1101)
+            widths.Add(wide);
+            widths.Add(narrow);
+            widths.Add(narrow);
+
+            return widths;
+        }
+
+        public static IReadOnlyList<int> EncodeCodabar(string value)
+        {
+            // Wikipedia table mapping (bars: 1=wide, spaces: 0=wide) for the standard symbol set.
+            // Ensure start/stop are present; default to A ... B if missing.
+            var raw = (value ?? string.Empty).Trim().ToUpperInvariant();
+            if (raw.Length == 0)
+            {
+                throw new ArgumentException("Codabar requires a non-empty value.");
+            }
+
+            bool HasStartStop(string s)
+            {
+                if (s.Length < 2) return false;
+                bool isStart = s[0] == 'A' || s[0] == 'B' || s[0] == 'C' || s[0] == 'D';
+                bool isStop = s[s.Length - 1] == 'A' || s[s.Length - 1] == 'B' || s[s.Length - 1] == 'C' || s[s.Length - 1] == 'D';
+                return isStart && isStop;
+            }
+
+            var text = HasStartStop(raw) ? raw : $"A{raw}B";
+
+            static (string spaceBits, string barBits) Map(char ch) => ch switch
+            {
+                '0' => ("001", "0001"),
+                '1' => ("001", "0010"),
+                '2' => ("010", "0001"),
+                '3' => ("100", "1000"),
+                '4' => ("001", "0100"),
+                '5' => ("001", "1000"),
+                '6' => ("100", "0001"),
+                '7' => ("100", "0010"),
+                '8' => ("100", "0100"),
+                '9' => ("010", "1000"),
+                '-' => ("010", "0010"),
+                '$' => ("010", "0100"),
+                '.' => ("000", "0001"),
+                '/' => ("000", "0010"),
+                ':' => ("000", "0100"),
+                '+' => ("000", "1000"),
+                'A' => ("011", "0100"),
+                'B' => ("110", "0001"),
+                'C' => ("011", "0001"),
+                'D' => ("011", "0010"),
+                _ => throw new ArgumentException($"Codabar does not support character '{ch}'.")
+            };
+
+            const int narrow = 1;
+            const int wide = 3;
+
+            var widths = new List<int>(text.Length * 8);
+
+            for (int idx = 0; idx < text.Length; idx++)
+            {
+                var ch = text[idx];
+                var (spaceBits, barBits) = Map(ch);
+
+                // Bars: 4 bits, 1=wide
+                int BarWidth(int pos) => barBits[pos] == '1' ? wide : narrow;
+                // Spaces: 3 bits, 0=wide (per wikipedia mapping table)
+                int SpaceWidth(int pos) => spaceBits[pos] == '0' ? wide : narrow;
+
+                widths.Add(BarWidth(0));
+                widths.Add(SpaceWidth(0));
+                widths.Add(BarWidth(1));
+                widths.Add(SpaceWidth(1));
+                widths.Add(BarWidth(2));
+                widths.Add(SpaceWidth(2));
+                widths.Add(BarWidth(3));
+
+                // Inter-character narrow space (except after last char).
+                if (idx != text.Length - 1)
+                {
+                    widths.Add(narrow);
+                }
+            }
+
+            return widths;
+        }
+
+        static readonly string[] EanL = new[]
+        {
+            "0001101","0011001","0010011","0111101","0100011","0110001","0101111","0111011","0110111","0001011"
+        };
+        static readonly string[] EanG = new[]
+        {
+            "0100111","0110011","0011011","0100001","0011101","0111001","0000101","0010001","0001001","0010111"
+        };
+        static readonly string[] EanR = new[]
+        {
+            "1110010","1100110","1101100","1000010","1011100","1001110","1010000","1000100","1001000","1110100"
+        };
+        static readonly string[] Ean13Parity = new[]
+        {
+            "LLLLLL","LLGLGG","LLGGLG","LLGGGL","LGLLGG","LGGLLG","LGGGLL","LGLGLG","LGLGGL","LGGLGL"
+        };
+
+        static int ComputeEanCheckDigit(string digitsWithoutCheck)
+        {
+            // digitsWithoutCheck is 7/11/12 digits depending on symbology.
+            int sum = 0;
+            bool weight3 = true;
+            for (int i = digitsWithoutCheck.Length - 1; i >= 0; i--)
+            {
+                int d = digitsWithoutCheck[i] - '0';
+                sum += weight3 ? d * 3 : d;
+                weight3 = !weight3;
+            }
+            int mod = sum % 10;
+            return (10 - mod) % 10;
+        }
+
+        public static string EncodeEan13(string value, out string checksumText)
+        {
+            var digits = new string(value.Where(char.IsDigit).ToArray());
+            if (digits.Length != 12 && digits.Length != 13)
+            {
+                throw new ArgumentException("EAN-13 requires 12 or 13 digits.");
+            }
+
+            if (digits.Length == 12)
+            {
+                var check = ComputeEanCheckDigit(digits);
+                digits += check.ToString(CultureInfo.InvariantCulture);
+            }
+            else
+            {
+                var expected = ComputeEanCheckDigit(digits[..12]);
+                if (digits[12] - '0' != expected)
+                {
+                    throw new ArgumentException("Invalid EAN-13 check digit.");
+                }
+            }
+
+            checksumText = digits[^1].ToString();
+
+            int first = digits[0] - '0';
+            var parity = Ean13Parity[first];
+
+            var sb = new StringBuilder(95);
+            sb.Append("101");
+            // digits 2..7 (index 1..6)
+            for (int i = 1; i <= 6; i++)
+            {
+                int d = digits[i] - '0';
+                sb.Append(parity[i - 1] == 'G' ? EanG[d] : EanL[d]);
+            }
+            sb.Append("01010");
+            for (int i = 7; i <= 12; i++)
+            {
+                int d = digits[i] - '0';
+                sb.Append(EanR[d]);
+            }
+            sb.Append("101");
+            return sb.ToString();
+        }
+
+        public static string EncodeUpcA(string value, out string checksumText)
+        {
+            var digits = new string(value.Where(char.IsDigit).ToArray());
+            if (digits.Length != 11 && digits.Length != 12)
+            {
+                throw new ArgumentException("UPC-A requires 11 or 12 digits.");
+            }
+
+            if (digits.Length == 11)
+            {
+                var check = ComputeEanCheckDigit(digits);
+                digits += check.ToString(CultureInfo.InvariantCulture);
+            }
+            else
+            {
+                var expected = ComputeEanCheckDigit(digits[..11]);
+                if (digits[11] - '0' != expected)
+                {
+                    throw new ArgumentException("Invalid UPC-A check digit.");
+                }
+            }
+
+            checksumText = digits[^1].ToString();
+
+            var sb = new StringBuilder(95);
+            sb.Append("101");
+            for (int i = 0; i < 6; i++)
+            {
+                int d = digits[i] - '0';
+                sb.Append(EanL[d]);
+            }
+            sb.Append("01010");
+            for (int i = 6; i < 12; i++)
+            {
+                int d = digits[i] - '0';
+                sb.Append(EanR[d]);
+            }
+            sb.Append("101");
+            return sb.ToString();
+        }
+
+        public static string EncodeEan8(string value, out string checksumText)
+        {
+            var digits = new string(value.Where(char.IsDigit).ToArray());
+            if (digits.Length != 7 && digits.Length != 8)
+            {
+                throw new ArgumentException("EAN-8 requires 7 or 8 digits.");
+            }
+
+            if (digits.Length == 7)
+            {
+                var check = ComputeEanCheckDigit(digits);
+                digits += check.ToString(CultureInfo.InvariantCulture);
+            }
+            else
+            {
+                var expected = ComputeEanCheckDigit(digits[..7]);
+                if (digits[7] - '0' != expected)
+                {
+                    throw new ArgumentException("Invalid EAN-8 check digit.");
+                }
+            }
+
+            checksumText = digits[^1].ToString();
+
+            var sb = new StringBuilder(67);
+            sb.Append("101");
+            for (int i = 0; i < 4; i++)
+            {
+                int d = digits[i] - '0';
+                sb.Append(EanL[d]);
+            }
+            sb.Append("01010");
+            for (int i = 4; i < 8; i++)
+            {
+                int d = digits[i] - '0';
+                sb.Append(EanR[d]);
+            }
+            sb.Append("101");
+            return sb.ToString();
+        }
+
+        public static string EncodeIsbnAsEan13(string value, out string checksumText)
+        {
+            var raw = new string(value.Where(char.IsLetterOrDigit).ToArray()).ToUpperInvariant();
+            if (raw.Length == 10)
+            {
+                // ISBN-10 -> EAN-13: 978 + first 9 digits + EAN check
+                var core = raw[..9];
+                if (!core.All(char.IsDigit)) throw new ArgumentException("Invalid ISBN-10.");
+                return EncodeEan13("978" + core, out checksumText);
+            }
+            if (raw.Length == 13)
+            {
+                if (!raw.All(char.IsDigit)) throw new ArgumentException("Invalid ISBN-13.");
+                return EncodeEan13(raw, out checksumText);
+            }
+
+            throw new ArgumentException("ISBN requires 10 or 13 characters.");
+        }
+
+        public static string EncodeIssnAsEan13(string value, out string checksumText)
+        {
+            // ISSN EAN-13: 977 + first 7 digits + 00 + EAN check
+            var raw = new string(value.Where(char.IsLetterOrDigit).ToArray()).ToUpperInvariant();
+            if (raw.Length != 8) throw new ArgumentException("ISSN requires 8 characters.");
+            var core = raw[..7];
+            if (!core.All(char.IsDigit)) throw new ArgumentException("Invalid ISSN.");
+            return EncodeEan13("977" + core + "00", out checksumText);
+        }
+
+        public static (IReadOnlyList<RadzenBarcode.BarcodeRect> bars, double vbWidth) EncodePharmacode(string value, double barHeight, int quietZone)
+        {
+            // Pharmacode one-track: numbers 3..131070
+            var digits = new string(value.Where(char.IsDigit).ToArray());
+            if (!int.TryParse(digits, NumberStyles.None, CultureInfo.InvariantCulture, out var n))
+            {
+                throw new ArgumentException("Pharmacode requires a numeric value.");
+            }
+            if (n < 3 || n > 131070)
+            {
+                throw new ArgumentException("Pharmacode value must be in range 3..131070.");
+            }
+
+            var bars = new List<(int width, bool isWide)>();
+            while (n > 0)
+            {
+                if (n % 2 == 0)
+                {
+                    bars.Add((2, true));
+                    n = (n - 2) / 2;
+                }
+                else
+                {
+                    bars.Add((1, false));
+                    n = (n - 1) / 2;
+                }
+            }
+            bars.Reverse();
+
+            double x = Math.Max(0, quietZone);
+            var rects = new List<RadzenBarcode.BarcodeRect>(bars.Count);
+            foreach (var b in bars)
+            {
+                rects.Add(new RadzenBarcode.BarcodeRect(x, 0, b.width, barHeight));
+                x += b.width + 1; // 1 module gap
+            }
+
+            var vbWidth = x + Math.Max(0, quietZone);
+            if (vbWidth <= 0) vbWidth = 1;
+            return (rects, vbWidth);
+        }
+
+        // POSTNET digit encoding from Wikipedia (weights 7,4,2,1,0). 1=full bar, 0=half bar.
+        static readonly Dictionary<char, string> PostnetDigitBits = new Dictionary<char, string>()
+        {
+            ['0'] = "11000",
+            ['1'] = "00011",
+            ['2'] = "00101",
+            ['3'] = "00110",
+            ['4'] = "01001",
+            ['5'] = "01010",
+            ['6'] = "01100",
+            ['7'] = "10001",
+            ['8'] = "10010",
+            ['9'] = "10100",
+        };
+
+        public static (IReadOnlyList<RadzenBarcode.BarcodeRect> bars, double vbWidth) EncodePostnet(string value, double barHeight, int quietZone, out string checksumText)
+        {
+            var digits = new string(value.Where(char.IsDigit).ToArray());
+            if ((digits.Length != 5 && digits.Length != 9 && digits.Length != 11))
+            {
+                throw new ArgumentException("POSTNET requires 5, 9, or 11 digits (ZIP / ZIP+4 / Delivery Point).");
+            }
+
+            int sum = digits.Sum(ch => ch - '0');
+            int check = (10 - (sum % 10)) % 10;
+            checksumText = check.ToString(CultureInfo.InvariantCulture);
+
+            var payload = digits + checksumText;
+
+            double fullH = barHeight;
+            double halfH = barHeight / 2.0;
+            double halfY = fullH - halfH;
+
+            double x = Math.Max(0, quietZone);
+            var rects = new List<RadzenBarcode.BarcodeRect>();
+
+            // Start frame bar (full)
+            rects.Add(new RadzenBarcode.BarcodeRect(x, 0, 1, fullH));
+            x += 2; // bar(1) + space(1)
+
+            foreach (var ch in payload)
+            {
+                var bits = PostnetDigitBits[ch];
+                for (int i = 0; i < 5; i++)
+                {
+                    bool full = bits[i] == '1';
+                    rects.Add(full
+                        ? new RadzenBarcode.BarcodeRect(x, 0, 1, fullH)
+                        : new RadzenBarcode.BarcodeRect(x, halfY, 1, halfH));
+                    x += 2;
+                }
+            }
+
+            // Stop frame bar (full)
+            rects.Add(new RadzenBarcode.BarcodeRect(x, 0, 1, fullH));
+            x += 1;
+
+            var vbWidth = x + Math.Max(0, quietZone);
+            if (vbWidth <= 0) vbWidth = 1;
+            return (rects, vbWidth);
+        }
+
+        // RM4SCC patterns and symbol matrix from Wikipedia:
+        // Top patterns (values 1..6) and Bottom patterns (values 1..6) are:
+        // 1=0011, 2=0101, 3=0110, 4=1001, 5=1010, 6=1100
+        static readonly string[] Rm4Patterns = new[] { "0011", "0101", "0110", "1001", "1010", "1100" };
+
+        // Matrix indexed by [topValue-1, bottomValue-1]
+        static readonly char[,] Rm4Matrix = new char[6, 6]
+        {
+            { '0', '1', '2', '3', '4', '5' },
+            { '6', '7', '8', '9', 'A', 'B' },
+            { 'C', 'D', 'E', 'F', 'G', 'H' },
+            { 'I', 'J', 'K', 'L', 'M', 'N' },
+            { 'O', 'P', 'Q', 'R', 'S', 'T' },
+            { 'U', 'V', 'W', 'X', 'Y', 'Z' }
+        };
+
+        static readonly Dictionary<char, (string top, string bottom)> Rm4CharToBits = BuildRm4CharToBits();
+
+        static Dictionary<char, (string top, string bottom)> BuildRm4CharToBits()
+        {
+            var dict = new Dictionary<char, (string top, string bottom)>();
+            for (int r = 0; r < 6; r++)
+            {
+                for (int c = 0; c < 6; c++)
+                {
+                    dict[Rm4Matrix[r, c]] = (Rm4Patterns[r], Rm4Patterns[c]);
+                }
+            }
+            return dict;
+        }
+
+        public static (IReadOnlyList<RadzenBarcode.BarcodeRect> bars, double vbWidth) EncodeRm4scc(string value, double barHeight, int quietZone, out string checksumText)
+        {
+            var text = new string(value.Where(char.IsLetterOrDigit).ToArray()).ToUpperInvariant();
+            if (string.IsNullOrEmpty(text))
+            {
+                throw new ArgumentException("RM4SCC requires alphanumeric input.");
+            }
+
+            // Only symbols present in the Wikipedia table (0-9, A-Z).
+            foreach (var ch in text)
+            {
+                if (!(ch is >= '0' and <= '9') && !(ch is >= 'A' and <= 'Z'))
+                {
+                    throw new ArgumentException($"RM4SCC does not support character '{ch}'.");
+                }
+            }
+
+            // Compute checksum per Wikipedia: sum top values and bottom values separately, mod 6, 0 => 6.
+            int sumTop = 0;
+            int sumBottom = 0;
+            foreach (var ch in text)
+            {
+                if (!Rm4CharToBits.TryGetValue(ch, out var bits))
+                {
+                    throw new ArgumentException($"RM4SCC does not support character '{ch}'.");
+                }
+                int t = Array.IndexOf(Rm4Patterns, bits.top) + 1;
+                int b = Array.IndexOf(Rm4Patterns, bits.bottom) + 1;
+                sumTop += t;
+                sumBottom += b;
+            }
+
+            int topVal = sumTop % 6;
+            topVal = topVal == 0 ? 6 : topVal;
+            int bottomVal = sumBottom % 6;
+            bottomVal = bottomVal == 0 ? 6 : bottomVal;
+
+            var checkChar = Rm4Matrix[topVal - 1, bottomVal - 1];
+
+            checksumText = checkChar.ToString();
+
+            // Encode start + data + checksum + stop.
+            // Start/stop are single bars; we use ascender for start and descender for stop.
+            double h = barHeight;
+            double third = h / 3.0;
+            double trackerY = third;
+            double trackerH = third;
+
+            RadzenBarcode.BarcodeRect BarRect(double x, bool top, bool bottom)
+            {
+                return (top, bottom) switch
+                {
+                    (false, false) => new RadzenBarcode.BarcodeRect(x, trackerY, 1, trackerH), // tracker
+                    (true, false) => new RadzenBarcode.BarcodeRect(x, 0, 1, trackerY + trackerH), // ascender (top + tracker)
+                    (false, true) => new RadzenBarcode.BarcodeRect(x, trackerY, 1, h - trackerY), // descender (tracker + bottom)
+                    (true, true) => new RadzenBarcode.BarcodeRect(x, 0, 1, h), // full
+                };
+            }
+
+            double xPos = Math.Max(0, quietZone);
+            var rects = new List<RadzenBarcode.BarcodeRect>();
+
+            // Start bar (ascender)
+            rects.Add(BarRect(xPos, top: true, bottom: false));
+            xPos += 2;
+
+            void AddSymbol(char ch)
+            {
+                var (topBits, bottomBits) = Rm4CharToBits[ch];
+                for (int i = 0; i < 4; i++)
+                {
+                    bool top = topBits[i] == '1';
+                    bool bottom = bottomBits[i] == '1';
+                    rects.Add(BarRect(xPos, top, bottom));
+                    xPos += 2;
+                }
+            }
+
+            foreach (var ch in text) AddSymbol(ch);
+            AddSymbol(checkChar);
+
+            // Stop bar (descender)
+            rects.Add(BarRect(xPos, top: false, bottom: true));
+            xPos += 1;
+
+            var vbWidth = xPos + Math.Max(0, quietZone);
+            if (vbWidth <= 0) vbWidth = 1;
+            return (rects, vbWidth);
+        }
+
+        public static string EncodeMsiPlessey(string value, out string checksumText)
+        {
+            var digits = new string(value.Where(char.IsDigit).ToArray());
+            if (digits.Length == 0) throw new ArgumentException("Plessey (MSI) requires numeric input.");
+
+            // Mod 10 (Luhn) check digit (common)
+            int check = ComputeLuhnCheckDigit(digits);
+            checksumText = check.ToString(CultureInfo.InvariantCulture);
+            digits += checksumText;
+
+            // MSI map from Wikipedia.
+            static string DigitMap(char d) => d switch
+            {
+                '0' => "100100100100",
+                '1' => "100100100110",
+                '2' => "100100110100",
+                '3' => "100100110110",
+                '4' => "100110100100",
+                '5' => "100110100110",
+                '6' => "100110110100",
+                '7' => "100110110110",
+                '8' => "110100100100",
+                '9' => "110100100110",
+                _ => throw new ArgumentException("MSI requires numeric input.")
+            };
+
+            var sb = new StringBuilder();
+            sb.Append("110"); // start
+            foreach (var ch in digits) sb.Append(DigitMap(ch));
+            sb.Append("1001"); // stop
+            return sb.ToString();
+        }
+
+        static int ComputeLuhnCheckDigit(string digits)
+        {
+            int sum = 0;
+            bool dbl = true;
+            for (int i = digits.Length - 1; i >= 0; i--)
+            {
+                int d = digits[i] - '0';
+                if (dbl)
+                {
+                    d *= 2;
+                    if (d > 9) d -= 9;
+                }
+                sum += d;
+                dbl = !dbl;
+            }
+            return (10 - (sum % 10)) % 10;
+        }
+
+        public static IReadOnlyList<int> EncodeTelepen(string value, out string checksumText)
+        {
+            // Telepen algorithm per Wikipedia: even parity bytes, little-endian bit order, modulo-127 checksum.
+            var bytes = Encoding.ASCII.GetBytes(value ?? string.Empty);
+
+            int sum = 0;
+            for (int i = 0; i < bytes.Length; i++)
+            {
+                if (bytes[i] > 0x7F) throw new ArgumentException("Telepen supports ASCII only.");
+                sum = (sum + bytes[i]) % 127;
+            }
+
+            int check = (127 - sum) % 127;
+            checksumText = check.ToString(CultureInfo.InvariantCulture);
+
+            // Build payload: start '_' + data + checksum byte + stop 'z'
+            var payload = new List<byte>(bytes.Length + 3) { (byte)'_' };
+            payload.AddRange(bytes);
+            payload.Add((byte)check);
+            payload.Add((byte)'z');
+
+            // Build bit stream LSB-first with even parity bit as MSB.
+            var bitStream = new List<int>(payload.Count * 8);
+            foreach (var b0 in payload)
+            {
+                int b = b0 & 0x7F;
+                int ones = CountBits(b);
+                int parityBit = (ones % 2 == 0) ? 0 : 1; // make total even
+                int byteWithParity = b | (parityBit << 7);
+
+                for (int i = 0; i < 8; i++)
+                {
+                    bitStream.Add((byteWithParity >> i) & 1);
+                }
+            }
+
+            // Encode bit stream into bar/space widths (narrow=1, wide=3).
+            // We produce alternating bar/space widths list, starting with bar.
+            const int narrow = 1;
+            const int wide = 3;
+            var widths = new List<int>();
+
+            int idx = 0;
+            while (idx < bitStream.Count)
+            {
+                if (bitStream[idx] == 1)
+                {
+                    // "1" => narrow bar, narrow space
+                    widths.Add(narrow);
+                    widths.Add(narrow);
+                    idx += 1;
+                    continue;
+                }
+
+                // starts with 0
+                if (idx + 1 < bitStream.Count && bitStream[idx + 1] == 0)
+                {
+                    // "00" => wide bar, narrow space
+                    widths.Add(wide);
+                    widths.Add(narrow);
+                    idx += 2;
+                    continue;
+                }
+
+                if (idx + 2 < bitStream.Count && bitStream[idx] == 0 && bitStream[idx + 1] == 1 && bitStream[idx + 2] == 0)
+                {
+                    // "010" => wide bar, wide space
+                    widths.Add(wide);
+                    widths.Add(wide);
+                    idx += 3;
+                    continue;
+                }
+
+                // General block 0 1^k 0 with k>=2
+                if (idx + 3 >= bitStream.Count || bitStream[idx] != 0 || bitStream[idx + 1] != 1)
+                {
+                    throw new ArgumentException("Invalid Telepen bit stream.");
+                }
+
+                int j = idx + 1;
+                while (j < bitStream.Count && bitStream[j] == 1) j++;
+                if (j >= bitStream.Count || bitStream[j] != 0)
+                {
+                    throw new ArgumentException("Invalid Telepen bit stream.");
+                }
+
+                int k = j - (idx + 1); // number of 1s
+                if (k < 2) throw new ArgumentException("Invalid Telepen bit stream.");
+
+                // leading "01" => narrow bar, wide space
+                widths.Add(narrow);
+                widths.Add(wide);
+
+                // middle extra 1s (k-2) => narrow bar, narrow space
+                for (int m = 0; m < k - 2; m++)
+                {
+                    widths.Add(narrow);
+                    widths.Add(narrow);
+                }
+
+                // trailing "10" => narrow bar, wide space
+                widths.Add(narrow);
+                widths.Add(wide);
+
+                idx = j + 1;
+            }
+
+            return widths;
+        }
+
+        static int CountBits(int v)
+        {
+            int c = 0;
+            while (v != 0)
+            {
+                c += v & 1;
+                v >>= 1;
+            }
+            return c;
         }
     }
 }
+
+

Radzen.Blazor/RadzenChart.razor.cs

@@ -55,9 +55,9 @@ namespace Radzen.Blazor
         /// <summary>
         /// Gets or sets the color scheme used to assign colors to chart series.
         /// Determines the palette of colors applied sequentially to each series when series-specific colors are not set.
-        /// Available schemes include Pastel (default), Palette, Monochrome, and custom color schemes.
+        /// Available schemes include Pastel, Palette (default), Monochrome, and custom color schemes.
         /// </summary>
-        /// <value>The color scheme. Default uses the Pastel scheme.</value>
+        /// <value>The color scheme. Default uses the Palette scheme.</value>
         [Parameter]
         public ColorScheme ColorScheme { get; set; }
 

Radzen.Blazor/RadzenDataFilterItem.razor

@@ -189,8 +189,6 @@ else if (Filter != null)
         }
         Filter.FilterValue = null;
 
-        Filter.Type = property.FilterPropertyType;
-
         var defaultOperator = typeof(System.Collections.IEnumerable).IsAssignableFrom(property.FilterPropertyType) ? FilterOperator.Contains : default(FilterOperator);
 
         if (property.GetFilterOperators().Any(o => o == property.FilterOperator))

Radzen.Blazor/RadzenDataGrid.razor

@@ -502,7 +502,7 @@
                                         else
                                         {
                                             <input autocomplete="off" aria-label=@(column.Title + FilterValueAriaLabel + column.GetFilterValue()) disabled=@(!column.CanSetFilterValue()) id="@(getFilterInputId(column))" @onchange="@((args) => OnFilter(args, column))" @onkeydown="@((args) => OnFilterKeyPress(args, column))" value="@column.GetFilterValue()" type="text" placeholder="@column.GetFilterPlaceholder()" class="rz-textbox" style="width: 100%;" />
-                                            @if (column.GetFilterValue() != null && filters.Any(d => d.Property == column.Property && $"{d.FilterProperty}" == $"{column.FilterProperty}"))
+                                            @if (column.GetFilterValue() != null && filters.Any(d => d.Property == column.Property && d.FilterProperty == column.FilterProperty))
                                             {
                                                 <i @onclick="@((args) => ClearFilter(column))" class="notranslate rzi rz-cell-filter-clear" style="position:absolute;inset-inline-end:10px;">close</i>
                                             }

Radzen.Blazor/RadzenDataGrid.razor.cs

@@ -10,7 +10,6 @@ using System.Collections.ObjectModel;
 using System.Collections.Specialized;
 using System.Globalization;
 using System.Linq;
-using System.Linq.Dynamic.Core;
 using System.Text.Json;
 using System.Threading.Tasks;
 
@@ -893,7 +892,7 @@ namespace Radzen.Blazor
             }
         }
 
-        async Task ToggleColumns()
+        void ToggleColumns()
         {
             if (selectedColumns == null)
             {
@@ -907,13 +906,8 @@ namespace Radzen.Blazor
                 c.SetVisible(selected.Contains(c));
             }
 
-            await PickedColumnsChanged.InvokeAsync(new DataGridPickedColumnsChangedEventArgs<TItem>() { Columns = selected });
+            PickedColumnsChanged.InvokeAsync(new DataGridPickedColumnsChangedEventArgs<TItem>() { Columns = selected });
             SaveSettings();
-
-            if (QueryOnlyVisibleColumns)
-            {
-                await Reload();
-            }
         }
 
         /// <summary>
@@ -1633,13 +1627,6 @@ namespace Radzen.Blazor
         [Parameter]
         public int ColumnsPickerMaxSelectedLabels { get; set; } = 2;
 
-        /// <summary>
-        /// Gets or sets a value indicating whether only visible columns are included in the query.
-        /// </summary>
-        /// <value><c>true</c> if only visible columns are included; otherwise, <c>false</c>.</value>
-        [Parameter]
-        public bool QueryOnlyVisibleColumns { get; set; }
-
         /// <summary>
         /// Gets or sets the column picker all columns text.
         /// </summary>
@@ -2029,8 +2016,7 @@ namespace Radzen.Blazor
                     }
                 }
 
-                return QueryOnlyVisibleColumns ? view
-                    .Select(allColumns.Where(c => c.GetVisible() && !string.IsNullOrEmpty(c.Property)).Select(c => c.Property)) : view;
+                return view;
             }
         }
 
@@ -2510,7 +2496,7 @@ namespace Radzen.Blazor
 
         internal Tuple<GroupRowRenderEventArgs, IReadOnlyDictionary<string, object>> GroupRowAttributes(RadzenDataGridGroupRow<TItem> item)
         {
-            var args = new Radzen.GroupRowRenderEventArgs() { Group = item.Group, FirstRender = firstRender, Expandable = item.GroupResult.Count > 0 };
+            var args = new Radzen.GroupRowRenderEventArgs() { Group = item.Group, FirstRender = firstRender };
 
             if (GroupRowRender != null)
             {
@@ -3590,59 +3576,6 @@ namespace Radzen.Blazor
                 }
             }
 
-            if (expandedItems != null)
-            {
-                expandedItems.Clear();
-            }
-
-            if (editedItems != null)
-            {
-                editedItems.Clear();
-            }
-
-            if (editContexts != null)
-            {
-                editContexts.Clear();
-            }
-
-            if (childData != null)
-            {
-                childData.Clear();
-            }
-
-            if (selectedItems != null)
-            {
-                selectedItems.Clear();
-            }
-
-            if (rowSpans != null)
-            {
-                rowSpans.Clear();
-            }
-
-            if (columns != null)
-            {
-                columns.Clear();
-            }
-
-            if (allPickableColumns != null)
-            {
-                allPickableColumns.Clear();
-            }
-
-            if (allColumns != null)
-            {
-                allColumns.Clear();
-            }
-
-            if (childColumns != null)
-            {
-                childColumns.Clear();
-            }
-
-            _value = null;
-            Data = null;
-
             GC.SuppressFinalize(this);
         }
 

Radzen.Blazor/RadzenDataGridColumn.razor.cs

@@ -1310,7 +1310,7 @@ namespace Radzen.Blazor
 
         internal bool HasCustomFilter()
         {
-            return GetFilterOperator() == FilterOperator.Custom && !string.IsNullOrEmpty(GetCustomFilterExpression());
+            return GetFilterOperator() == FilterOperator.Custom && GetCustomFilterExpression() != null;
         }
 
         internal bool HasActiveFilter()