Apr 13, 2021 · Apr 12, 2021 · Apr 12, 2021 · Apr 12, 2021 · Apr 12, 2021 · Apr 12, 2021
diff --git a/src/libraries/System.IO.FileSystem/tests/FileStream/FileStreamConformanceTests.cs b/src/libraries/System.IO.FileSystem/tests/FileStream/FileStreamConformanceTests.cs
            Assert.Equal(2, stream.Length);
            Assert.Equal(2, createdFromHandle.Length);
        }

        [Fact]
        public async Task WriteByteFlushesTheBufferWhenItBecomesFull()
        {
            string filePath;
            List<byte> writtenBytes = new List<byte>();

            using (FileStream stream = (FileStream)await CreateWriteOnlyStreamCore(Array.Empty<byte>()))
            {
                filePath = stream.Name;

                stream.WriteByte(0);
                writtenBytes.Add(0);

                byte[] bytes = new byte[BufferSize - 1];
                stream.Write(bytes.AsSpan());
                writtenBytes.AddRange(bytes);

                stream.WriteByte(1);
                writtenBytes.Add(1);
            }

            byte[] allBytes = File.ReadAllBytes(filePath);
            Assert.Equal(writtenBytes.ToArray(), allBytes);
        }
    }

    public class UnbufferedSyncFileStreamStandaloneConformanceTests : FileStreamStandaloneConformanceTests
Original file line number	Diff line number	Diff line change
Expand Up		@@ -161,6 +161,31 @@ public async Task LengthIsNotCachedAfterHandleHasBeenExposed(FileAccess fileAcce
		Assert.Equal(2, stream.Length);
		Assert.Equal(2, createdFromHandle.Length);
		}

		[Fact]
		public async Task WriteByteFlushesTheBufferWhenItBecomesFull()
		{
		string filePath;
		List<byte> writtenBytes = new List<byte>();

		using (FileStream stream = (FileStream)await CreateWriteOnlyStreamCore(Array.Empty<byte>()))
		{
		filePath = stream.Name;

		stream.WriteByte(0);
		writtenBytes.Add(0);

		byte[] bytes = new byte[BufferSize - 1];
Copy link Member danmoseleyApr 12, 2021 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. Is it worth putting something other than zeros in here? So it's distinct from the first byte you wrote Copy link Contributor carlossanlopApr 12, 2021 Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. Doesn't really matter. What matters is that we are attempting to write an 11th character on the stream when the buffer can only hold 10 characters. danmoseley reacted with thumbs up emoji Copy link Member jozkeeApr 12, 2021• edited Loading Choose a reason for hiding this comment The reason will be displayed to describe this comment to others.Learn more. ...and the problem was that the internal buffer is not being reset/flushed when WriteByte is called when this buffer is already full.
		stream.Write(bytes.AsSpan());
		writtenBytes.AddRange(bytes);

		stream.WriteByte(1);
		writtenBytes.Add(1);
		}

		byte[] allBytes = File.ReadAllBytes(filePath);
		Assert.Equal(writtenBytes.ToArray(), allBytes);
		}
		}

		public class UnbufferedSyncFileStreamStandaloneConformanceTests : FileStreamStandaloneConformanceTests
Expand Down