def test_SuccessResponseFormatter(self):
        """
        Test that the thing that spits out POP3 'success responses' works
        right.
        """
        self.assertEqual(
            pop3.successResponse(b'Great.'),
            b'+OK Great.\r\n')

        Test that the thing that spits out POP3 'success responses' works
        right.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_pop3.py