I never said jet aircraft, I said piston as per my first post. In regards to the daily/crew change tests stated above, of course they are daily/crew change - the aircraft types specify that and have the technology to show a failure.
But for piston, with no technology other than the runup to show a busted magneto, fouling, etc, I think you're mad to run up, shut down, come back a few hours later and fly with no further check. Older piston engines are ugly on startup, and I've had cases where thats messed with the mags (funnily enough after a mag check in the hangar). If I had just said I'd already flown it that day lets fly who knows what could have happened.