I have finished the test levels. I think I took 1 hour solving Advanced air control, and 15 minutes beating everything else, but I guess that's expected from a bonus bonus level.
I believe level 4 might be bit confusing because normally pressing a colored button toggles the corresponding springs, but in this particular example you are given the opportunity to hold 2 buttons of the same color and when that happens they act more as a ON/OFF switch rather than a toggle because holding 2 red buttons at the same time is the same as holding one. The stage is not particularly difficult but I don't remember encountering this interaction before.
Level 7 introduces a mechanic I consider noteworthy because for the first time a fairy other than the blue one is capable of enraging the toads. Of course, this was technically introduced earlier along with the brave fairy, but this is the first time it's required to solve the level.
I know I'm reading too much into it but this has slightly changed my perception of the blue fairy's character from mischievous to maybe a little compulsive because annoying the toads without poking them doesn't progress the levels. That means poking is more important.
Finally, there's a new unfinished mechanic in the form of the mysterious red area that attracts the friendly toads. This generally works fine with the exception of stage 12 where the yellow toad would sometimes get stuck walking right instead of up where it's supposed to go and I couldn't really tell why.
Besides that I think the levels were quite straightforward and I didn't find any bugs or issues. The reason I had difficulties with Advanced air control in particular was because I didn't occur to me that I had to enrage the toad at the start rather than later on so I kept misusing the smart fairy to go in rather than out which left me short of a fairy to press the red button at the end.
Keep up the good work.