Re: Frustration about testing
I would stick with it if I were you. In dojo #2 you quit just before you would have tested, it seems, so don't make that mistake this time!
In Aikido, even three years is a relatively short period. I don't think you were unfairly treated if you were advised not to test with just over the minimum. Also, I think it's inevitable to lose some ability with a 1+ year break, you were on break for a long time.
This is not a race, you know. Frustration over testing is normal. Some of the best students look back and say they were not tested as soon as they wished. To quit because you were not advised to test with only the minimum requirements, to lose your enjoyment of the sport because of not testing hurts only yourself.
You probably need a full year to train before your next test, in my opinion. Imagine you are starting from the beginning, and really apply yourself. Forget your bitterness about how long you've been practicing and how little you have to show for it. Maybe you'll be tested faster than normal the next time. Maybe not, but if you are really good, no one can take that away from you.