I did GP-Zero at Jerez the first year of the 800s. Now Jerez is the last test again, I'm seriously thinking about another trip. Last time we broke into the circuit (found a gap in the fence) and camped at the top of the hill. Not sure if I'm up for that kind of guerilla camping again.
"GP-Zero" was a timed practice of one hour at the final test session before the season starts. It used to get TV coverage and I think that year even the BBC carried it. I don't think the name was official but that's what the journos called it.