15years ago, I was working in an overhaul shop in France, on PT6 and PW100 engines. there were two engine test cells. the old one for small PT6 serie and 1800CA3 was using a short propeller. But due to the propeller blast, it was not very easy to go the noisy room to detect dynamic leaks.
The new one was using a hydromechanical shaftbrake for the large PT6 series and PW100 series. Everything was static and quiete in the room (exept the noise), really more comfortable to have a look.