Some Psychology tests are taken at the start of the turn phase. For example, Terror tests caused by terrifying creatures within 6 and Stupidity tests are both taken at the start of the turn. Other tests, caused by special rules, spells, etc, are also taken at the start of the turn phase. When a player is called upon to take different tests at the start of the turn, then do them in the order they are listed here:
Other (caused by special rules, spells etc)
So, if a unit is obliged to take a Terror test and a Stupidity test, take the Terror test first, and only if this is passed will it be necessary to take the Stupidity test.