We used to do it frequently on Whirlwinds & Wessex. Since the blade tracking could be affected by wind gusting, on one occasion, at Leconfield, in 1971, we did it INSIDE No 5 hangar, with hangar doors fully open, and a Mk6 Alvis 6-wheel fire tender in attendance.
It was done by riggers, (airframe tradesmen), and often in conjunction with post-scheduled maintenance runs. I recall one such was in mid-winter, on a snow-covered tie-down pan. It went on for some time, the riggers freezing from the rotor-induced blizzard. I was an engine fitter at the time, so opened the engine access door, while it was running, and basked, to the riggers' chagrin, in the warm airflow around the efflux, all the time smiling like a cheshire cat! - NOBODY loves a smart-ar$e!