def test_credInterfacesProvidesLists(self):
        """
        When two C{--auth} arguments are passed along which support the same
        interface, a list with both is created.
        """
        options = DummyOptions()
        options.parseOptions(['--auth', 'memory', '--auth', 'unix'])
        self.assertEqual(
            options['credCheckers'],
            options['credInterfaces'][credentials.IUsernamePassword])

        When two C{--auth} arguments are passed along which support the same
        interface, a list with both is created.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/cred/test/test_strcred.py