def test_failureAlreadySet(self):
        """
        Captured failures in the new style do not step on a pre-existing
        old-style C{"failure"} key.
        """
        failure = Failure(RuntimeError("Weak salsa!"))
        event = self.eventWithFailure(failure=failure)
        self.assertIs(event["failure"], failure)

        Captured failures in the new style do not step on a pre-existing
        old-style C{"failure"} key.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/logger/test/test_legacy.py