does your engine die while you are driving, or do the rpms suddenly drop for a second while you are driving? if it does either one of those, its probably your ignitor. if your car has over 100,000 miles on it, you might want to just replace the ignitor and see if that solves it.
if you want to actually test it, you should get a haynes or chilton manual and an electrical voltage tester. you will have to measure electric current between certain terminals of the ignitor.