def test_import(self):
        """
        Every public class in twisted.mail.pop3client should be available as a
        member of twisted.mail.pop3 with the exception of
        twisted.mail.pop3client.POP3Client which should be available as
        twisted.mail.pop3.AdvancedClient.
        """
        publicClasses = [c[0] for c in inspect.getmembers(
                                       sys.modules['twisted.mail.pop3client'],
                                       inspect.isclass)
                         if not c[0][0] == '_']

        for pc in publicClasses:
            if not pc == 'POP3Client':
                self.assertTrue(hasattr(twisted.mail.pop3, pc))
            else:
                self.assertTrue(hasattr(twisted.mail.pop3,
                    'AdvancedPOP3Client'))

        Every public class in twisted.mail.pop3client should be available as a
        member of twisted.mail.pop3 with the exception of
        twisted.mail.pop3client.POP3Client which should be available as
        twisted.mail.pop3.AdvancedClient.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_pop3client.py