It does, because somebody might have done something to the filesystem between your test and the rest of your code. This is why I found your "Defensive Programm

It does, because somebody might have done something to the filesystem between your test and the rest of your code. This is why I found your "Defensive Programming 101 really" comment slightly arrogant (perhaps I misunderstood the intention). Writing correct programs is not easy and one should not mock others, because there is always something new to learn.