I really don't understand what is going on here with this `__done__` approach.  It seemed cleaner when the tests simply relied on returning a promise (or not, for tests that previously only cared about brute force synchronous performance).  As @novemberborn mentions above, I'm wary that trying to coordinate the completion of a test by using this kind of "done" mechanism may not be foolproof, whereas relying on the promises themselves would be.