Flight simulator check rides are difficult and stressful. They will last four hours and test basic flying skills and multiple emergency situations. These occur every six months with one being a recurrent training session and the other being a FAA check ride. If a pilot has problems in the check ride he cannot fly again until he receives extra training and is later certified.
These check rides require a lot of studying beforehand and some memorization of aircraft systems and emergency procedures. There is also some tension and nervousness since a pilot is putting his job on the line with every check-ride but it is always a good learning experience.