Remove the spark plug, re-attach the coil wire to it and somehow ground the plug to the engine block. Kick it over and watch the plug for sparks.
Or, you can make a little spark checker. Get any old clean spark plug and a metal clamp or large alligator clip. Solder the spark plug's threads to the clamp and clip it to a convenient ground. Now you don't have to remove the plug in the head or wonder if it is clean enough to spark.. Just attach the coil wire to the one with the clamp.