How to avoid taking "uneeded" tests?

[cookderosa]

you're asking how to know if an exam duplicates credit, which means that it won't get counted twice.

That's a great question.

So, the answer for EVERY EXAM will sit with the college that awards the credit. If you transfer, you'll have the same situation.
For instance, let's say you take CLEP Biology.
Your college awards 8 credits and counts it as BIO101 with lab (4cr) and BIO102 with lab (4 cr.)
the college down the street may award 6 credits in the science elective category SCI199 (6 cr.)
and a college in the state next to yours may award you 3 BIO credits for BIO102, as long as you already have earned credit in BIO101.

In short, the duplication is impossible for some just to tell you- you have to find out which exams your college accepts, and which course equivalencies go with the exams. If it's not on your college's website, then contact someone in advising and ask them to SEND YOU the list via email (you'll want it in writing). In addition, though 50 is a passing score, sometimes colleges use different scores for different courses- so you might see something like "score of 50 = 3 credits, a score of 60 = 4 credits" or such.