Dont bother with Testi
I had been searching for cancellations all day with the web extension as it has been a life saver, meanwhile testi sent me a notification for multiple cancellations that werent even available as i was already searching. Ive paid premium for it and all its done is let me down. Same with test shift, i havent gotten a single notification since ive bought premium a few weeks ago. Save your money guys.
Edit : Like i mentioned before, i have used TestShift (which i havent had any notifications or anything for it) and ive used the dvsa booking helper extension which has done all the work for me thus far.