def test_multipleStopListening(self):
        """
        It is safe and a no-op to call L{TuntapPort.stopListening} more than
        once with no intervening L{TuntapPort.startListening} call.
        """
        self.port.startListening()
        self.port.stopListening()
        second = self.port.stopListening()
        self.reactor.advance(0)
        self.assertIsNone(self.successResultOf(second))

        It is safe and a no-op to call L{TuntapPort.stopListening} more than
        once with no intervening L{TuntapPort.startListening} call.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/pair/test/test_tuntap.py