Twisted.trial unittests have an additional feature where if they return a deferred, the deferred will be waited on until completed. This behaviour is present in the base TestCase class twisted.trial.unittest.TestCase. These deferreds are not currently waited on in py.test.
Additionally, some twisted unittests are presented as generators decorated by twisted.internet.defer.inlineCallbacks in which yield yields a deferreds. These generators should be iterated to completion and all generators waited upon for completion.
This is just a placeholder, as I should investigate this myself, and add more information to this ticket.