I know its a bit redneck and not a GREAT indication of quality of spark, but when I'm working alone(all the time lol) and testing for spark, I will aim timing light at windshield to see if it flashes.
pull the plug out of the head. Rig it to a good ground with the spark plug wire still attached. Make sure you can see the electrode good while cranking the engine over. What does your spark at the plug look like?