How do you check car alternators?

"Checking" Car Alternators

In my area [SE Texas] all of the national chain [Autozone, O'Reilly, and Advance for example] automotive parts stores have hand held portable test devices which they attach to my car in their parking lot. They do not charge for these services; they are free.

These devices can check my alternator, battery, auto electrical system, and even the on-board computers.

In the case of your alternator, these tests do more than just check for output voltage.