def test_UIDListLineFormatter(self):
        """
        Test that the function which formats lines in response to a UIDL
        command does so appropriately.
        """
        uids = ['abc', 'def', 'ghi']
        listLines = list(pop3.formatUIDListResponse([], uids.__getitem__))
        self.assertEqual(
            listLines,
            [b'+OK \r\n', b'.\r\n'])

        listLines = list(pop3.formatUIDListResponse([123, 431, 591],
                         uids.__getitem__))
        self.assertEqual(
            listLines,
            [b'+OK \r\n', b'1 abc\r\n', b'2 def\r\n', b'3 ghi\r\n', b'.\r\n'])

        listLines = list(pop3.formatUIDListResponse([0, None, 591],
                         uids.__getitem__))
        self.assertEqual(
            listLines,
            [b'+OK \r\n', b'1 abc\r\n', b'3 ghi\r\n', b'.\r\n'])

        Test that the function which formats lines in response to a UIDL
        command does so appropriately.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_pop3.py