you can do the non smart way test it like I did(not recommended but I didnt really care) start car, pull the positive cable and see if the car stays on.
On new cars doing this will turn off the car as there are failsafes, but not in the e46.
take it to an alternator shop/ independent
"Player-haters turning bitch like they have vaginas ‘Cause we see them dollar signs and let the cash blind us.
Money'll brainwash you and leave your ass mindless..When snakes slither in the grass spineless.."