Prepare changes for support of Flush(bool flushToDisk) in System.IO.Abstractions

Author: vbtig

Source/Testably.Abstractions.Testing/FileSystem/FileStreamMock.cs

@@ -189,6 +189,10 @@ public override void Flush()
 		InternalFlush();
 	}
 
+	/// <inheritdoc cref="FileSystemStream.Flush(bool)" />
+	public override void Flush(bool flushToDisk)
+		=> Flush();
+
 	/// <inheritdoc cref="FileSystemStream.FlushAsync(CancellationToken)" />
 	public override Task FlushAsync(CancellationToken cancellationToken)
 	{

Tests/Testably.Abstractions.Tests/FileSystem/FileStream/Tests.cs

@@ -162,6 +162,22 @@ public void Flush_ShouldNotChangePosition(
 		stream.Position.Should().Be(2);
 	}
 
+	[SkippableTheory]
+	[InlineAutoData(false)]
+	[InlineAutoData(true)]
+	public void Flush_WriteToDisk_ShouldNotChangePosition(
+		bool flushToDisk, string path, byte[] bytes)
+	{
+		using FileSystemStream stream = FileSystem.File.Create(path);
+		stream.Write(bytes, 0, bytes.Length);
+		stream.Seek(2, SeekOrigin.Begin);
+		stream.Position.Should().Be(2);
+
+		stream.Flush(flushToDisk);
+
+		stream.Position.Should().Be(2);
+	}
+
 	[SkippableTheory]
 	[AutoData]
 	public void Flush_ShouldNotUpdateFileContentWhenAlreadyFlushed(