--add-to-time-stamps doesn't work at least with filenametimestamp module

[novoid]

See disabled unit tests starting with test_add_to_time_stamps_good_case() in https://github.com/novoid/Memacs/blob/master/memacs/tests/filenametimestamps_test.py

When enabled and run, it ends up in:

filenametimestamps_test.py:162: in call_add_to_time_stamps
    return memacs.test_get_entries()
../lib/memacs.py:216: in test_get_entries
    data = self.test_get_all()
../lib/memacs.py:205: in test_get_all
    self.__init(test=True)
../lib/memacs.py:86: in __init
    self._parser_parse_args()
../filenametimestamps.py:76: in _parser_parse_args
    Memacs._parser_parse_args(self)
../lib/memacs.py:167: in _parser_parse_args
    self._args = self._parser.parse_args(self.__argv)
../lib/argparser.py:166: in parse_args
    "to ,e.g., \"+1\" or \"-3\".")
/usr/lib/python3.5/argparse.py:2394: in error
    self.exit(2, _('%(prog)s: error: %(message)s\n') % args)

Maybe somebody wants to investigate.