from django.core.exceptions import ValidationError

class ValidationAssertions:

    def assertFailsValidation(self, clean, failed_fields, **kwargs):

        with self.assertRaises(ValidationError) as cm:

            clean(**kwargs)

        self.assertEqual(sorted(failed_fields), sorted(cm.exception.message_dict))

    def assertFieldFailsValidationWithMessage(self, clean, field_name, message):

        with self.assertRaises(ValidationError) as cm:

            clean()

        self.assertIn(field_name, cm.exception.message_dict)

        self.assertEqual(message, cm.exception.message_dict[field_name])