A volt meter will tell you if its dead as a doornail as they say.. but it won't test if it can actually put out any amps. The auto parts stores around here (autozone, advance) will test them in the vehicle, for free.
The autoparts store will put the alternator in a "Growler." This will not only test the output, but the regulator (if internally regulated) but the bearings as well. The tester should vary the speed of the spin. This will test the bearings. All in all, take the time to remove the alternator and have it tested... then you know what's right, and what's wrong.