Fitness testing helps personal trainers assess their clients in order to set attainable goals. Depending upon the person, there are a variety of tests you could do. You could put your client on a treadmill and have them complete the Bruce Test, watching their heart rate and testing for heart problems. You could also try the Harvard Step Test, timing the client as they step up and down a platform for three minutes. Be sure to familiarize yourself with the different cardio endurance tests.