If the powerhead has been damaged due to being run partially out of water, it would have burnt up. At the very least, it would show some visible signs of its demise. To see if the powerhead works, just don't have your hand in the water with it when testing, and just make sure the powerhead is completely submerged. There's nothing special to look for; either it works or it doesn't.
So long as your testing it safely, you have nothing to fear.
As Matt said, it's probably fine.
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90G. Kent Phos Reactor running carbon and PhosBan, Coral Life 225 Skimmer, Typhoon 5 Stage RO/DI, 20 Gal Sump/Refugium with Chaetomorpha lit opposite daylight cycle. Coralife 2x150MH+2x96W PC Actinics, Ecotech Vortech propeller pump, Hydor Koralia #3. |