Tell him the test doesn't have any diagnosis affect. Meaing it's not there to diagnose someone, only to make aware possible traits that should be looked at by a professional. My doctor put me an anti-psychotic recently to help with the voices that I hear daily. Just try to convince him, however it is his life and well being and unless he becomes violent or suicidal, its 100% up to him if he wants to take it or not. Just my 2 cents.