Not to be the safety police or anything since I've personally done way dumber things with my quad but holding it with props on is asking for trouble. When bench testing *always* take your props off. The ESC can get a signal it interprets as "go full throttle" at an point in time for whatever reason (coronal mass ejections or cosmic radiation the least likely but actually no joke still possible for it to flip a bit that makes things go wrong). More likely you have "cross talk" or signals going down one wire that cause EM radiation that is picked up in other nearby wires and can cause things to go haywire.... long story short there's like 1000 ways this can go wrong and if it does the thing can tilt hard and props can cut you badly.
Regarding motors spooling up and down, if you are testing the thing held down or otherwise sitting on a bench with props off where it has no ability to actually correct it's position then you should expect the motors to spool up and down a bit if arming it since the quad is "trying" to get to level or to achieve some target angle based on the input it's getting from the receiver. Long story short you should expect it to spin up the motors at a slightly variable speed if it is actually armed since it is attempting to level itself and uses the fact that it "knows" where each motor is (in the FC programming is baked into the mixer settings).
I'll put down my clipboard after this, but anytime testing it hooked up to a computer or holding onto the quad make sure props are off. If testing it with props on make sure you have Transmitter on first you plug the quad in on the ground somewhere away from other people, walk back to Transmitter or back up a bit before arming in case things go awry on arming or take off. Until you're confident in the FPV system and quad itself I would always take off line of sight then drop goggles down onto my face (also if taking off with goggles on supposed to have a spotter but at very least use good judgment).