Ask your local auto parts store to do it.
Charge it, replace it,test the alternator,Charge it, replace it,test the alternator,
Most alternator or battery shops will test it for free.
Car would either have to be running or alternator removed for bench test
run it and then disconnect the negative wire from the battery if alternator dies its bad.
I pulled the negative cable from the battery with the truck running and the engine quit. Is this a test to see if the alternator needs to be replaced?
with a voltmeter
Either drive to your local auto parts store and have them test it in the vehicle or you can remove the alternator and take it to your local auto parts store and they can bench test it for you.
Shops like Advance will test it for free.
Full fielding is a diagnostic test of the alternator You make the alternator work full out and measure the voltage and amperage output to test it against a published specification.
Take it out, and to the nearest Autozone and they will test it free of charge.
Battery light usually means alternator not charging. Most common solutions would be be a bad alternator, bad connection, or loose alternator belt. If the battery and alt test ok than check the connections to the alternator and battery.
The alternator must be running to test without disassembly. If you remove it, many auto part stores will test at no charge. One test is a voltage test. Start the engine and use a multimeter to check the voltage at the battery. It should read between 13.5 and 16 volts. Any less or more and the alternator is bad.