The way I've always done it in my R44 is, having completed mag checks to manually wind on throttle to test the RPM horn. The throttle is then shut to split the needles. I then turn on the governor and slowly wind on the throttle manually until 80% when the governor takes over and automatically takes it up to 102% (in the R44). This ensures that the governor is in control all the way so ensuring no overspeed and excercising the governor over its full range.