87 RX7 Alternator?

Well i had my car checked at the local auto parts to see if my alternator was working fine and told me i need to replace it but i drove for awhile and my battery level doesnt go down and is around 12 just a little higher than 12 on the level gauge in the dash. I was also thinking that if i needed an alternator if my light of the battery will go on warning me but it does not.

System voltage should be at 14.5v with the car running. Why did you have the alternator tested?

well i had a dead battery about a week ago i got it charged and it was good for about 5 days and just today i had a dead battery again so it turned out it is the alternator and i just bought it online...