def test_all(self):
        """
        This test checks that all names listed in
        twisted.mail.pop3.__all__ are actually present in the module.
        """
        mod = twisted.mail.pop3
        for attr in mod.__all__:
            self.assertTrue(hasattr(mod, attr))

        This test checks that all names listed in
        twisted.mail.pop3.__all__ are actually present in the module.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_pop3.py