public async Task CanAdvanceWithPartialConsumptionOfFirstSegment(int firstWriteLength)
{
Writer = new StreamPipeWriter(Stream, MinimumSegmentSize, new TestMemoryPool(maxBufferSize: 20000));
await Writer.WriteAsync(Encoding.ASCII.GetBytes("a"));
var memory = Writer.GetMemory(firstWriteLength);
Writer.Advance(firstWriteLength);
memory = Writer.GetMemory();
Writer.Advance(memory.Length);
await Writer.FlushAsync();
Assert.Equal(firstWriteLength + memory.Length + 1, Read().Length);
}