After finding that the coil does not fire in test mode but before blaming the driver transistor, the ground path to the coil should be verified. Take a test lead with one end clipped to ground and momentarily touch the metal tab of the driver transistor. If the coil fires then the ground path is good and the driver transistor is likely bad. If the coil doesn't fire, then either the ground path is faulty OR there isn't voltage to the coil.