A dyno for days is a little exteme but they are looking for the weakest links. My engines saw a couple hours of WOT on the dyno. I have been told they will run them WOT for up to 5 hours looking for failure.

Actually runing a motor at 85% all day long is not that bad. However Flying one in and out of the water with constant throttle adjustments combined with the pounding is not that good.