Improved assertion error messages in validators tests

    if expected is not None and issubclass(expected, Exception):

        test_mask = 'test_%s_raises_error_%d'

        def test_func(self):

            self.assertRaises(expected, validator, value)

            # assertRaises not used, so as to be able to produce an error message

            # containing the tested value

            try:

                validator(value)

            except expected:

                pass

            else:

                self.fail("%s not raised when validating '%s'" % (

                    expected.__name__, value))

    else:

        test_mask = 'test_%s_%d'

        def test_func(self):

            try:

                self.assertEqual(expected, validator(value))

            except ValidationError as e:

                self.fail("Validation of '%s' failed. Error message was: %s" % (

                    value, str(e)))

    if isinstance(validator, types.FunctionType):

        val_name = validator.__name__

    else: