The point of the test was to distinguish between a human and an animal :-/
REVEREND MOTHER: I hold at your neck the gom jabbar. Don’t pull away or you’ll feel that poison. A Duke’s son must know about many poisons—this one kills only animals.
PAUL: Are you suggesting a Duke’s son is an animal?
REVEREND MOTHER: Let us say I suggest you may be human. Your awareness may be powerful enough to control your instincts. Your instincts will be to remove your hand from the box. If you do so you will die.
The point of the test was to distinguish between a human and an animal :-/