I often just add this in case I need it. I don't think it hurts to leave it in there, as that way if some tests create files in the future, we can just append them to this list and they'll get cleaned up in ``tearDown``. If I remove this, I have to also remove the code that would clean them up in ``tearDown``, so leaving it all just makes it easier for the future.

The files all get created under ``self.test_out``, which gets added to ``self.dirs_to_remove``, so we don't need to worry about those.