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
"We've come a long long way together, through the hard times and the good. I have to celebrate you baby, I have to praise you like I should...
I have to praise you like I should.."