errebepe, Thanks for the comments. I incorporated your suggestions about the test case. It will now check explicitly for DistutilsFileError and calls self.fail() if it gets this exception. I removed parens in "if (src_dir)" as well.

I considered "plen = len(src_dir)+1 if src_dir else 0" form but I found it difficult to follow compared to an explicit "if".

As to adding a docstring to the test case, I vaguely remember seeing some comment about not having docstrings in test functions. I also don't find docstrings in any of the test functions (found with a quick look at less test_*.py output).