You can test a coil for spark using two D cells in series , that’s 3 Volts. Not saying that you are stressing the coil but at least see if it sparks. I use the simple jury rigged tester that mimics the Mertronic vibrator that member Ray Schaber presented in an "Outboarder" tech article , January 2004 issue. A set of old points, a condenser, home made cam and spin it up with a drill motor.
Joe B