def test_listDoesNotDisplayDuplicates(self):
        """
        The list for C{--help-auth} does not duplicate items.
        """
        authTypes = []
        options = DummyOptions()
        for cf in options._checkerFactoriesForOptHelpAuth():
            self.assertNotIn(cf.authType, authTypes)
            authTypes.append(cf.authType)

        The list for C{--help-auth} does not duplicate items.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/cred/test/test_strcred.py