If ya go to a electrical distributor they got wand testers. Basically the thing beeps or lights up if it's near 110v or greater. Test inside the cover plate on your switch and make sure that's getting power and if it is, then go into the attic and test the line leading to the fixture. No power at the fixture means you got a bad switch and if you do have power then you got a bad fixture. The only thing with these testers is that if there are power lines crossing they do pick up on the bleed though every now and then. ALWAYS assume that lines are hot for safety!
Warning though, electricity can kill so if your real unsure, nervous...leave it to someone that knows! Better to be a live toker than a dead grower!!! Good luck and STAY SAFE!! :thumbsup: