def test_removeNonExistentSystemEventTrigger(self):
        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:]))
make sure that it finds the graph head correctly
dataset/ETHPy150Open kuri65536/python-for-android/python-modules/twisted/twisted/test/test_internet.py/SystemEventTestCase.test_removeNonExistentSystemEventTrigger--crossover with--dataset/ETHPy150Open Mouse-Imaging-Centre/pydpiper/pydpiper_testing/test_simple_pipeline.py/TestSimplePipeline.test_graph_head