Some real fundamentals of auto electrical testing missing here guys.

A) Use multi meter and obtain a battery reference voltage, no pint in measuring the alternator if you have no idea what the battery voltage is. Measure the battery (20v scale over the battery terminal everything switched off) If you have not got over 12v stay here until you have - recharge the battery to begin with.

B) When the ignition is switched on (eng off) does the battery light illuminate? if not you will not excite the alternators field current, believe it or not, that battery light is very important!

C) If the battery light illuminated (ign on) start the car, at the 8mm bolt(13mm nut size) measure the voltage right from the alternator to the battery negative, this should be around 14v (eng running)

If you can meet all the above with positive outcomes e.g. battery at 12v, battery light working ign off, extinguishes when engine running the it will be the alternator, providing the alternator is being driven correctly mechanically.

When the free wheeling clutch fails the alt looks like its spinning, the pulley will be spinning but loss of drive the alternator rotor will occur.

I think that should just about do it!