public void ReadFileChunkTest_WorksFine()
{
// arrange
var filePath = @"C:\temp\in.txt";
var fileData = new MockFileData("test data");
var startPosition = 5L;
var chunkLength = 4;
mockFileSystem.AddFile(filePath, fileData);
// act
var actualBytes = target.ReadFileChunk(filePath, startPosition, chunkLength);
var actual = Encoding.ASCII.GetString(actualBytes);
// assert
Assert.Equal("data", actual);
}