ADHD is actually one of the things that’s actually rigorously and quickly testable (assuming you’re willing to take self-reported effects / observations, you can’t read a number off a lab test) but it’s never done because it involves giving someone without any medical diagnosis a schedule 2 drug and we moralize that for some reason.
You just give the person a stimulant and see what happens. If they get really awake, hyperactive, excited, anxious, shaky, hyperfocused, etc. then nope, if they get calm, content, or sleepy then yes. And it’s not like this is crazy in general, we do “just treat it and see if they get better” as the test for plenty of things.
Nobody bats an eye when we do the same thing for depression, it’s super common for people who exhibit the symptoms to be asked to try a few antidepressants and see if they work.
I get that some people abuse stimulants but they suuuuuuck. Life changing because they allow you to function but you will also curse them for it. The side effects are awful. So much so that I tried a bunch of non-stimulant medications until I found one that worked. Nobody who doesn’t have ADHD is gonna wanna regularly take adderall or vyvanse just because it would be miserable and that’s before the fact that they aren’t cheap.
Edit: /rant Mental health is wild because smart and well meaning people designed a system that actively prevents people from being honest and getting help. Want to talk to your therapist about your suicidal thoughts, bulimia, or self-harm, nope. Not unless you want to take a mandatory grippy sock vacation away from your support network and get set back in school or lose your job all things famous for improving mental health. Wanna tell your psychologist that you think you might have ADHD because you were at a party, tried something and it made you felt way different than everyone else, haha drug seeker.