Doubt that it would be a dry run to test response. They generally set off the bomb shortly after leaving. And leaving an ID card would not be helpful. Even if the bag was stolen, it could still lead back to someone, as they might have CCTV of the bag being taken.
Also, a dry run would make authorities more cautious, so the data obtained would be useless.
Maybe a crazy mainlander who thought a shrine would be a good place to leave a bag for the day.