The Wizard Test by Hilari Bell

Dayven wants with all his heart to become a Guardian but then he passes the Wizard Test. Wizards are distrusted by the Guardians, the protectors of Tharn. Dayven’s cousin and best friend, Soren, will soon take the Guardian’s oath. Dayen is told he has a choice as long as he doesn’t heal a person with his magic, he can take the Guardian’s oath. But first he is sent on a mission for the Guardians to spy on his newly appointed wizard teacher, Reddick.