def test_get_parser_filename(self):
parser = get_parser()
options = parser.parse_args(['filename'])
self.assertEqual(options.input, 'filename')
def assert_get_parser_error(self, args, expected, mock_stderr):
parser = get_parser()
with self.assertRaises(SystemExit):
parser.parse_args(args)
self.assertIn(expected, mock_stderr.write.call_args[0][0])