If you have a tx like the Futaba 9c or 10C, not sure about others, it will have a servo test function that moves all servos to full travel on both extreemes. It will run as long as you want it to and is very useful in finding intermentent servos, although they will not be carring the flight load they normally would see.

I had a case a couple years back on one plane that the ailerons seemed to not stay trimmed, I sat the plane on a bench and ran the servo test for 30 minutes and the trim was still good at the end, then Iran another five minutes and applied hand resistance on the ailerons. It turns out that I had one servo that was "slipping" for the lack of a better term. Removed it and tied my dead servo knot in the cord and put it in the dead servo pile. Read servo spare parts bin.

I'm seriously thinking of one of the smaller "testers" listed above, if nothing else for setting upnew plane centers.

Don