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
"To my seeds, may I lead you into no breed of evil. In the categories and stories I breed my sequel.
You know the money brews, blunts, and broken 22's. Monkey see, monkey do, shorty sipping sunny dew.."