The most brutal test protocol I have ever done is the Sufferfest/Wahoo 4DP Full Monty:-

Warm-up, 2x10s all-out sprints, 5 min VO2 max interval, very brief rest, 20 min FTP interval and finally a 1 min flat out anaerobic interval.

You definitely need to be in the right frame of mind to complete this test at your true potential! I aborted it once during the FTP interval because I was just mentally broken. I can only face this test once or twice per year and have avoided it altogether for the last 2 years! But when I have managed to nail it I have always been surprised how deep I could actually go.

A few years back I read an interview with the guy who had just won the national hill climb championship and he said that he probably won because he was the only one puking up after crossing the finish line!