My problem with this is that your example replies on you already knowing the correct answer, so that you know it’s given you the wrong answer and you can go back and try to trick it into giving a different answer. If you’re asking it a question to which you don’t already know the answer, how would you know if this has happened?

It’s ending because it’s old. JET has been running since the 80s. It’s successor is ITER, which ran into some delays, but is expected to be finished sometime next year.