In previous games, I was always under the assumption that when you encountered a fear-inducing foe, you tested once for fear the moment you met him/her/it. If you passed, you're fine. If you failed, then you dealt with whatever the result was. Either way, there was only the one fear test.
However, on page 277 for Black Crusade, when describing multiple fear-inducing foes, there's the note "In other words, they [the Heretics] must only make one Fear Test each Round."
So, we normally make a fear test every round? This seems pretty brutal, because unless the target is immune in some fashion, eventually everyone will fail and cause havoc. Also, it would make those insanity tests far more common.