If it makes you feel any better I don't feel ready either. In fact every single person who is up for dan testing I've talked to at the dojo doesn't feel ready. We just have to trust sensei's judgement. He wouldn't put us up for it if he didn't think we could do it.
Relax, train in earnest, and do your best. That's all you can do.
To answer your original question; IMO, no you shouldn't feel completely ready to test. A little nervousness is good for us and I think that if you feel 100% prepared then you've waited too long.