Hi, I've had experience of both, whilst in the military after an eng replacement we always did an airtest iaw the AP 5M flight test manual (oh the good ol' days).
Now I'm a licensed engineer we do full power ground runs then hand it over back into revenue service. The only exceptions to this are after big checks as dictated by the Maint manual which I think says an airtest or handling check (theres a difference) is reqd if a number of engs/ control surfaces have been removed/refitted/replaced.
Its an expensive game flight testing Ac, and as we all know the military has deep pockets. I'm on 4 eng ac at the moment. hope it helps
bodjit