Add GCF tests

BinaryObjectScanner.Test/FileType/GCFTests.cs

@@ -0,0 +1,33 @@
+using System.IO;
+using BinaryObjectScanner.FileType;
+using Xunit;
+
+namespace BinaryObjectScanner.Test.FileType
+{
+    public class GCFTests
+    {
+        private static readonly SabreTools.Serialization.Wrappers.GCF wrapper
+            = new(new SabreTools.Data.Models.GCF.File(), new MemoryStream(new byte[1024]));
+
+        [Fact]
+        public void DetectFile_EmptyString_Null()
+        {
+            string file = string.Empty;
+            var detectable = new GCF(wrapper);
+
+            string? actual = detectable.Detect(file, includeDebug: false);
+            Assert.Null(actual);
+        }
+
+        [Fact]
+        public void DetectStream_EmptyStream_DefaultValue()
+        {
+            Stream? stream = new MemoryStream();
+            string file = string.Empty;
+            var detectable = new GCF(wrapper);
+
+            string? actual = detectable.Detect(stream, file, includeDebug: false);
+            Assert.Equal("AACS (Unknown Version)", actual);
+        }
+    }
+}