def test_secondaryExplicitPort(self):
        """
        An argument of the form C{"ip:port/domain"} can be used to specify an
        alternate port number for which to act as a secondary.
        """
        options = Options()
        options.parseOptions(['--secondary', '1.2.3.4:5353/example.com'])
        self.assertEqual(
            [(('1.2.3.4', 5353), ['example.com'])], options.secondaries)

        An argument of the form C{"ip:port/domain"} can be used to specify an
        alternate port number for which to act as a secondary.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_tap.py