I have to disagree that we don't need this test.

Of course, by looking at the source code we can easily make the assumption that this should work (if we happen to look at only the line where `io.open` is used), but there are often times when the issue is actually much more involved and our initial guess is wrong (even if it seems obvious).

Furthermore, tests act as specifications what to expect from certain routines without looking at the actual source code.