I’m going to say that as you perform more clinical tests typically your chances of a wrong diagnosis will decrease proportionally. However particularly in the case of ADHD tests, if you know the test questions and the symptom description I think you could cheat your way to a diagnosis. If you went to all of these tests in earnest, without looking them up, just providing spontaneous responses, and all of them come back positive, I’d say chances are you have ADHD.