Experiment testing

Test scenarios:

Simultaneous_Sessions: The worker tries to accept a HIT when there is another HIT registered to him.

Session_overlap: A previous worker started a game and then returned the HIT. In this case, the HIT cannot be re-used.

Too_many_sessions: The worker cannot accept another HIT based on the limit of the number of HITs per worker.

Too_many_fails: The worker has failed the quiz too many times, and he can no longer work on any HIT.