def test_removeRemovedTrigger(self):
        """
        L{_ThreePhaseEvent.removeTrigger} should raise L{ValueError} the second
        time it is called with an object returned by
        L{_ThreePhaseEvent.addTrigger}.
        """
        handle = self.event.addTrigger('before', self.trigger, self.arg)
        self.event.removeTrigger(handle)
        self.assertRaises(ValueError, self.event.removeTrigger, handle)

        L{_ThreePhaseEvent.removeTrigger} should raise L{ValueError} the second
        time it is called with an object returned by
        L{_ThreePhaseEvent.addTrigger}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_internet.py