def test_removeNonExistentSystemEventTrigger(self):
        """
        Passing an object to L{IReactorCore.removeSystemEventTrigger} which was
        not returned by a previous call to
        L{IReactorCore.addSystemEventTrigger} or which has already been passed
        to C{removeSystemEventTrigger} should result in L{TypeError},
        L{KeyError}, or L{ValueError} being raised.
        """
        b = self.addTrigger('during', 'test', lambda: None)
        self.removeTrigger(b)
        self.assertRaises(
            TypeError, reactor.removeSystemEventTrigger, None)
        self.assertRaises(
            ValueError, reactor.removeSystemEventTrigger, b)
        self.assertRaises(
            KeyError,
            reactor.removeSystemEventTrigger,
            (b[0], ('xxx',) + b[1][1:]))

        Passing an object to L{IReactorCore.removeSystemEventTrigger} which was
        not returned by a previous call to
        L{IReactorCore.addSystemEventTrigger} or which has already been passed
        to C{removeSystemEventTrigger} should result in L{TypeError},
        L{KeyError}, or L{ValueError} being raised.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_internet.py