Reddit reviews The Adult ADHD Tool Kit: Using CBT to Facilitate Coping Inside and Out

Tuckman has two books on adult ADHD:

More Attention, Less Deficit: Lots of text but split into bite-sized chapters to make it easy to dip in and out, whatever sections interest you. If you read it all the way through it will seem repetitive, but that's intentional. Still my favorite general book on adult ADHD, maybe tied with the Ramsay/Rostain book The Adult ADHD Toolkit.

Understand Your Brain, Get More Done: A workbook, with much less text and lots of space for writing to do the exercises. I haven't gotten that much out of it since it contains basically the same strategies as the first one, but doing exercises can help you tailor them to your own life and get your thinking clearer. Maybe I should give it another chance.

By all means read Hallowell/Ratey! Hallowell is very enthusiastic, but he really knows what he's talking about and doesn't go overboard like the people going on about hunters and farmers, all the advantages of ADHD, we are just right and the rest of the world is wrong, etc.

Tuckman, Barkley and Ramsay/Rostain all emphasize the problems and challenges of ADHD more (and in more detail what to do about them). Whether you call that "realistic" or "pessimistic" may be a matter of perspective.

Essentially a psychologist or psychiatrist asks you lots of questions. There isn't a scan or biological test, the diagnosis is based on your behaviour and history.

I think the one my doctor used was the Wender-Utah rating scale - it's a lot of questions but only some of them are relevant to the diagnosis.

http://www1.psykiatristod.se/Global/Psykiatristod/Bilagor/ADHD/WURS_ADHD_.pdf

edit to add: actually the first thing I did, a year before getting formally diagnosed, was get a copy of the Adult ADHD Toolkit which really helped me, and continues to help.

https://www.amazon.com/Adult-ADHD-Tool-Kit-Facilitate-ebook/dp/B00N3SUGLO