add more tests

tests/SharpCompress.Test/GZip/GZipWriterNonSeekableTests.cs

@@ -0,0 +1,73 @@
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using SharpCompress.Archives.GZip;
+using SharpCompress.Test.Mocks;
+using SharpCompress.Writers.GZip;
+using Xunit;
+
+namespace SharpCompress.Test.GZip;
+
+/// <summary>
+/// Regression tests for writing gzip streams to non-seekable (forward-only) output streams.
+/// GZip is inherently a single forward stream with no seek-dependent layout, so streaming to
+/// a <see cref="ForwardOnlyStream"/> must simply produce a valid, readable gzip stream.
+/// </summary>
+public class GZipWriterNonSeekableTests
+{
+    private const string EntryName = "content.txt";
+
+    private static byte[] CreateContent() =>
+        Encoding.UTF8.GetBytes(string.Concat(Enumerable.Repeat("Hello streaming gzip! ", 500)));
+
+    private static async Task<byte[]> WriteToNonSeekableAsync(byte[] content)
+    {
+        using var ms = new MemoryStream();
+        await using (var writer = new GZipWriter(new ForwardOnlyStream(ms)))
+        {
+            using var source = new MemoryStream(content);
+            await writer.WriteAsync(EntryName, source, null);
+        }
+        return ms.ToArray();
+    }
+
+    private static byte[] WriteToNonSeekableSync(byte[] content)
+    {
+        using var ms = new MemoryStream();
+        using (var writer = new GZipWriter(new ForwardOnlyStream(ms)))
+        {
+            using var source = new MemoryStream(content);
+            writer.Write(EntryName, source, null);
+        }
+        return ms.ToArray();
+    }
+
+    private static void AssertRoundTrips(byte[] gz, byte[] expected)
+    {
+        using var archive = GZipArchive.OpenArchive(new MemoryStream(gz));
+        var entry = archive.Entries.First();
+        using var extracted = new MemoryStream();
+        using (var entryStream = entry.OpenEntryStream())
+        {
+            entryStream.CopyTo(extracted);
+        }
+        Assert.Equal(expected, extracted.ToArray());
+    }
+
+    [Fact]
+    public async Task GZip_Async_NonSeekable_RoundTrips()
+    {
+        var content = CreateContent();
+        var gz = await WriteToNonSeekableAsync(content);
+        AssertRoundTrips(gz, content);
+    }
+
+    [Fact]
+    public void GZip_Sync_NonSeekable_RoundTrips()
+    {
+        var content = CreateContent();
+        var gz = WriteToNonSeekableSync(content);
+        AssertRoundTrips(gz, content);
+    }
+}