Hi, I ran into a problem with this test when the source was located in certain directories. The mkdir(2) man page states that the set-group-ID bit is inherited from the parent directory, but this test was written in such a way that it assumes the bit is unset. Whether that assumption is true depends on where the checkout lives, which leads to some people being able to reproduce the problem whereas others cannot. I think the correct fix is to exclude the bit from the check.
Making probinson a reviewer since they reviewed the original test.