I never got to do that. Got plenty of practice taping the instrumentation umbilical to the wing, fuselage, and emergency exit while the engine run guys (top of the shop pecking order) stood around and kibitzed. As a mechanic with a pilot's license, I was an alien Intruder in their hard core blue collar culture, and never got to do any of the "good stuff". I did get plenty of practice at tires, brakes, lav dumps, daily walk arounds, outdoor lamp replacements, and towing with an open tug in wintertime.. I go on engine runs on turboprops on a nightly basis tho.
I haven't seen an ATR or a Dash in years. All the service in these parts is Embraers, Canadairs, A320s, and the occasional 73. The ignorami flying public refer to anything with a prop on it as a "piston pounder" and protest loudly if asked to board one.
Cheers,
Wes