I made a brief video on the procedure I have used for many years here at the dealer that has not failed me yet in identifying a weak but functioning alternator causing many headaches like no starts after changing the battery and only checking the voltage output of the Alt. I hope this helps as there really isn't a need to take the alt off to get it tested. No fancy tools required.

 

Just another tid bit of info. What he says is correct, however if you have a slipping alternator belt the alternator will appear to be bad. Slipping belts do not always make any squealing noise and look perfectly normal. I have found that if the belt is slipping the alternator pulley will be VERY hot to the touch due to the slipping belt. If a V belt ever wears down to where it makes contact with the bottom of the pulley grove, its shot. V belts drive on the sides of the belt, not the bottom. If the V groove in the pulley at the bottom is polished, replace the belt. No matter how tight you make the belt, It will not drive the alternator properly
Hope that helps someone
Darryl...