I get the little $2 power test lights from walmart, and take the case off. Them i get an old stagepin connector and remove the ground pin. I stick the insides of the test light into the body of the connector with the lamp near the cable hole and connect the positive and negative leads on the light to the pins in the connector and close up the connector. Without the ground pin the connector will plug into a cable either way(saves time and hassle in the dark) and a quick look at the top(side away from the pins) tells if there's power. The only problem I have with it is that it's easy to lose in pockets full of tie light, lamps(new ones in boxes and blown), screwdrivers, wrenches, ect. (the usual troubleshooting stuff).
I made a bunch of 2P&G testers many years ago, using the guts of an off-the-shelf neon circuit tester.
All my current power testers used for cable and circuit testing, are simply a cheap neon tester for a standard Edison outlet, on a male 2P&G to f/m Edison adapter. This way I can still test Edison circuits when needed.
Remember to all that you can not test dimmer circuits with a neon tester, without having a resistive load in parallel, as the dimmers generally don't fire without a resistive load, while the neon needs at least 70 volts to operate.
Steve B.