On the 777 a Full power Take off is called after an engine change. The engine already has been test bed run and all parameters are recorded. After installation , Dry and Wet motor runs and idles are completed with checks of the Hydraulics and Electricals along with Anti-Ice. Pneumatics are checked at approx 80% N1 ( GE90) These checks are all completed by the Engineers .
The full power take off can be quite a handful when there are ATC height constraints !
First flight after engine change is naturally a ETOPS Verification flight.