def METHOD_NAME(self):
    """ Object date_update updated when attachment added """
    with freeze_time("2022-07-04T14:00:00+00:00"):
        # add attachment
        AttachmentFactory(content_object=self.object)
    self.object.refresh_from_db()
    # object date_update has been updated with current datetime
    self.assertEqual(self.object.date_update.isoformat(), "2022-07-04T14:00:00+00:00")