def test_multipleTransitionsFailure(self):
        """
        A L{MethodicalMachine} can only have one transition per start/event
        pair.
        """

        class WillFail(object):
            m = MethodicalMachine()

            @m.state(initial=True)
            def start(self):
                "We start here."
            @m.state()
            def end(self):
                "Rainbows end."

            @m.input()
            def event(self):
                "An event."
            start.upon(event, enter=end, outputs=[])
            with self.assertRaises(ValueError):
                start.upon(event, enter=end, outputs=[])

        A L{MethodicalMachine} can only have one transition per start/event
        pair.
        
stackoverflow/venv/lib/python3.6/site-packages/automat/_test/test_methodical.py