That's a fair point, and historically it was very hard to arrange to test a unit unless you were the manufacturer. So even a serious reviewer couldn't say "The FooCorp RescueMax failed after just six minutes in our ice water bath" or "Our testers weren't able to understand the orientation instructions for the FooCorp RescueMax and test transmissions were not received in the canyon test area" because they weren't supposed to try the actual function of the beacon at all.
I believe COSPAS SARSAT and the relevant US authorities got it together so that it is now possible to arrange a test carve out, agree with everybody when and where the units will be tested and not cause helicopters of annoyed rescuers to arrive so long as you stay in the agreed area and only test in the agreed time frame. But it can't be made trivial, so chances are only really hardcore survivalist outfits will do that work.
In the ResQLink manual it literally has you test it several times per year to verify correct operation. FWIW I've had mine 7 years and it's been through several battery replacements at the factory and been through several rough longer expeditions. No problems at all with the GPS test cycle.
I believe COSPAS SARSAT and the relevant US authorities got it together so that it is now possible to arrange a test carve out, agree with everybody when and where the units will be tested and not cause helicopters of annoyed rescuers to arrive so long as you stay in the agreed area and only test in the agreed time frame. But it can't be made trivial, so chances are only really hardcore survivalist outfits will do that work.