Test for ovulating? Day 10-11 and continue until you get a postive OPK. Or are you testing for pregnancy? I would wait until day 14 or later.
Ideally, you should wait to test until you've exceeded your normal luteal phase. So, if your luteal phase is normally 14 days, you should test at 15 dpo if no AF.
However, we all know how hard it is to wait that long (I usually give in at 12 or 13 dpo:-). Just keep in mind that if you do test, and get a negative, it could just be too early.
I think the earliest BFP I've seen on here was at 9 dpo. I've also seen some at 11 and 12 dpo.