def test_NoTransition(self):
        """
        A L{NoTransition} exception describes the state and input symbol
        that caused it.
        """
        # NoTransition requires two arguments
        with self.assertRaises(TypeError):
            NoTransition()

        state = "current-state"
        symbol = "transitionless-symbol"
        noTransitionException = NoTransition(state=state, symbol=symbol)

        self.assertIs(noTransitionException.symbol, symbol)

        self.assertIn(state, str(noTransitionException))
        self.assertIn(symbol, str(noTransitionException))

        A L{NoTransition} exception describes the state and input symbol
        that caused it.
        
stackoverflow/venv/lib/python3.6/site-packages/automat/_test/test_core.py