I've used this test scenario in the past, minus the spray bottle of water, and it's a good test for faulty/worn/old/crappy spark plug wiring and it's harness.

If there is arcing, anywhere in these runs, you should see it.

If you suspect this and go to move spark wires for a cleaner look, with the engine running, put on rubber gloves, cause you will act like a nice big ground and definitly feel the pain...lol...