It's a well defined procedure
For acceptance out of a heavy check, I have a magazine sized checklist about 3/4" thick that outlines a series of procedures that take around 8 hours if all goes well. We check everything from the interior lights to the emergency O2 bottles on the inside, then check everything on the outside, then we fly. The exterior preflight is obviously comprehesive. We check control surfaces for proper movement and travel, etc. The flight takes about 4 hours and consists of operation every system and operational parameter. We check control effectiveness, do stalls, check trim with the controls assisted and in manual reversion at high and low speed. We shut down the engines, restart the engines, start the APU, drop the gear with using every available method and run the flaps/slats in and out. We time every operation to ensure it meets specs. We test the autothrottles and the autopilot, we do numerous approaches and go arounds, coupled and hand flown, coupled misses and we also intentionally go below G/S to test the GPWS. We also intentionally sink after a miss to set off the "don't sink" function of the GPWS.
And much more.
The objective is to provide as close a flaw free airplane to the line guys as possible.
Hope this helps
8N