A Test Speaker is used in an evaluation contest. The Test Speaker gives a speech which is evaluated by all the contestants separately. After the speech, each evaluator is secluded away from the contest room until his turn to speak comes. That way the evaluators don't hear what the other evaluators have said.
The Test Speaker is usually chosen by the Contest Organizer and should normally be someone from outside the contest territory. Since not all contestants maybe expert evaluators, it is not necessary for the Test Speaker to give a perfect speech, since the evaluators will be expected to give some constructive criticism.