def test_datetime_config_validation(self):
        class TestConf(schema.Schema):
            item = schema.DateTimeItem(title="Item", description="Item description")

        try:
            jsonschema.validate(
                {"item": "2015-07-01T18:05:27+01:00"},
                TestConf.serialize(),
                format_checker=jsonschema.FormatChecker(),
            )
        except jsonschema.exceptions.ValidationError as exc:
            self.fail("ValidationError raised: {}".format(exc))

        with self.assertRaises(jsonschema.exceptions.ValidationError) as excinfo:
            jsonschema.validate(
                {"item": "3"},
                TestConf.serialize(),
                format_checker=jsonschema.FormatChecker(),
            )
        self.assertIn("is not a", excinfo.exception.message)