public void fill_copies_data_to_buffer_and_leaves_stream_in_correct_position()
{
var buffer = new byte[10];
var stream = CreateStream(buffer.Length);
Assert.True(stream.Fill(buffer, 0, buffer.Length));
for(int i = 0; i < buffer.Length; ++i)
{
Assert.Equal(i, buffer[i]);
}
Assert.Equal(stream.Position, buffer.Length);
}