Depends on the task. For code, ask it to implement a not-difficult but not-trivial feature. "Please add hooks to the AnkiDroid source code so that addons would be viable" might be a good start, for something that is on my mind. Then compare implementations.

For checking hallucinations, ask it about events and trivia that happened eons ago, and also within the last decade. Try some things that it can not possibly know, like how much celery Brad Pitt likes in his salad.