Right. It will be a (not insignificant) waste of money, but probably won't hurt your application as it's rarely required and only sometimes recommended. There is a practice test on the GRE site. Take that and see how you do on timing and which subjects to focus more heavily on.
I took the general bio GRE and got something like 96 percentile on the molecular portion, 87 on organismal, and something in lousy, maybe the 60's or 70's in the ecology/evolution portion (I have absolutely no interest in ecology). I still submitted it, as they actually send the sub-scores. I don't think it helped or hurt me, no one cared.