We've got a test that's been running fine ever since it was written a month or so ago. Now, it's failing intermittently on our CI (continuous integration) box, so I took a look.
It turns out it's a stupid test because it depends on pre-existing data in the database. But, the win is that while looking at the code to figure out why this was failing, I noticed a completely unrelated bug in the production code. See, unit testing helps find bugs :-) -- https://mail.python.org/mailman/listinfo/python-list
