Anytime an A&P mechanic wants to test the updates/fixes made to an aircraft's systems or any part for that matter, what are the laws (at least under the FAA) that legally allow them to operate an aircraft?
I've personally seen GA airplanes being taxied (in non-movement areas so far) by A&P mechanics. Is there a law that states that they can/cannot operate that very aircraft on a taxiway (movement area)?
What about larger aircraft (business jets, airliners etc.)? Do authorized mechanics always need a licensed (and appropriately certified with the required ratings) pilot all the time when testing the aircraft after repairs?
Finally, what about military jets? I once acquainted with someone who worked on military jets' electrical systems, but was never licensed to fly. Would he solely rely on the PIC's conclusion about the condition of the jet?