Old school testing is very effective.
While the engine is running hold a cold beer in one hand and then firmly Grasp each ignition wire with the other hand. If the can is crushed or dropped, you need new wires! The same concept applies to touching any part of the coil body. If it leaks energy, it should be replaced! Except exposed terminals...
As for as improving, you may get better bang per bike by adjusting the curve and rate as to when the spark fires vs the the actual hardware. Also, if the compression ratio has been increased, increased energy and smaller gap can help... But generally speaking a NEW coil isn't going to deliver more energy unless the whole system is updated (what ever components time and drive the coil(s).
Although the method mentioned works - I would not suggest it! Use a ground wire to a screw driver and **IF** there is leakage energy, let it go from the screw driver through the wire to the engine ground keeping you from getting ZAPPED! It pretty effective! Although so is misting subject parts w/a spray bottle of water! :thumbup: