Re: Who deems you ready to test?
it seems to vary dojo to dojo. The majority of dojos tend to go with a system of your instructor will let you know when you are ready, or that is how it appears to me.
the best bet is to join a dojo, start training and find out from fellow students or your instructor how it all works. each instructor and association have their own way of doing things and you will definately not be the first person that your instructor has met that is nervous about these things, so they will understand.
Enjoy your training (when you start)