I was talking about this only a few days ago, one of my friends was put in a situation on the sim which was incredibly wierd where the captain was making the approach when the auto pilot disengaged, bad weather conditions etc, engine failure then he was suddenly told that the captain was to remove himself from the controls while on final in a theoritic position that the captain had a heart or attack or similar so therefore the first officer was to take over immediatly, no completely sure of the details but it with multiple failures the landing was impossible, but he was simply told that it was test, he didnt need to land on the runway, is was to see how he would cope and how he could bring the aircraft as safely as possible. I thought it particularly wierd.