Just how are you making these test? You need two test. Test the spark plug under compression and your coil should throw a good 1/4 in. spark at the plug end of the plug wire. I will suggest just try a new spark plug they aren't very expensive and that will tell you if the plug is bad or not and that way you can eliminate that first test. If you don't get a good 1/4 in. spark then its a very good chance your coil is bad.