Not sure what you're working with, but here is a simple test good for most air cooled engines with flywheel mounted alternators; Every one I've seen had a printed circuit regulator mounted somewhere with a three wire flat connector of some sort. The center wire was the battery lead. Should read battery voltage with engine off(some need the key switch on but not all). No voltage indicates a blown fuse or bad connection somewhere. The two outside wires, often yellow, are the stator output and should have somewhere between 26 to 34 volts AC with engine running if the alternator is working. If you test with motor running and have no AC voltage, look for a stator issue. If AC voltage is good and center wire has battery voltage when running but less than 13v, replace the regulator.
