Here is a method of testing high-tension magnetos. I have experimented with many different types of magnetos from the popular WICO EK's to Maytag Eisemann's and the method works well with all of them.
To test the coil and condenser, simply proceed as follows:
Place one or two thicknesses of paper between the breaker points to insulate them. Then connect the high-tension wire to a grounded spark plug. Now, with a 6-volt lantern battery, attach a wire from a terminal of the battery to one breaker-point connection. A wire from the other battery terminal is 'scratched' against the other breaker-point connection. This will not damage the magneto. If the coil and condenser are in good condition, a fat spark will appear at the spark plug. If no spark appears at the plug and the connections have been made properly, then either the coil or condenser is at fault. The easiest way to determine which is faulty is to disconnect one side of the condenser from the circuit and temporarily connect a condenser known to be good across the condenser circuit. I say, "known to be good" because occasionally even a brand new condenser is faulty. If a spark now appears at the plug, obviously the old condenser is worn out. If there is no spark, the coil is of course suspect.
The simple test outlines here is by no means absolute for either a coil or condenser, especially the latter, may function perfectly when cold, yet, when warm or hot, may fail.