Why Michael Schumacher once tested a GP2 car

Before his F1 comeback with Mercedes in 2010, Michael Schumacher spent three days testing a GP2 car at Jerez. Given the differences between the pinnacle of the sport and the slower feeder series machinery, what was really in it for Schumacher, and what did GP2 get out of letting him drive its development car? We also take a look back at how Schumacher's performance in this test affected expectations ahead of his F1 race return