Flight test after engine change.
In days long ago when we had big round engines and long inline ones as well, we did indeed do a flight test after an engine change. But, I don't recall ever doing one on a jet for just an engine change.
These days turbine engines stay on the wing for so many years, and modules get changed in situ, so it is a whole different ball game. It all gets done at the run-up pad.
However in your case with several, or all, engines being off at once and being put back together I would think it was a prudent thing to do.
The wonderful Iron Duck, memories!! I believe you still have the 4 survivors of the ones that I flew in Africa??
Speedbird48