Note that all a psychiatrist does for adults to determine whether they have ADHD is give them a self-reporting questionnaire. You can find sample questionnaires and diagnostic criteria for interpreting them in a couple of places online. In other words, if you're honest with yourself when you answer, you can know exactly what a psychiatrist will say without having to go.

The one thing that might not be mentioned on such sites is that people being tested for ADHD are also given an inventory for anxiety disorders, sometimes mixed into the ADHD questions. Anxiety looks like ADHD in some ways but is treated differently; effectively, in order for an ADHD diagnosis to "count", you have to be not-overly-anxious.

In my case I had to take two questionnaires (one was 100+ questions for general mental disorder evaluation), a subset of an IQ test, and a computer test. The computer test was interesting... it was along the lines of left click when you see the number 2, right click when you hear a sound. No other distractions trying to trick you into clicking, but it is a 15 minute test. Excruciatingly boring, but even trying as hard as I could, the psychiatrist wondered if I had cheated/fudged the test because my results were so far out of whack compared to the IQ test.

You sure on that? It's extremely common for ADHD to be comorbid with anxiety. There's a challenge in figuring out which is secondary to which, sure (same with depression and ADHD or depression and anxiety--they all confound each other) but I've never heard of apparent anxiety being a disqualification.

Not a disqualification, no; it's more, like you said, that they confound one-another, but usually it's the anxiety doing more of the confounding. It's very hard to determine whether the ADHD really "exists" as its own thing or not until you've treated for the anxiety. (In neurochemical terms, since adrenaline production consumes dopamine, there's no way to know what the person's "normal" dopamine flow is like until you can get them to stop being so stressed out.)

Couple this with the fact that a good few of the psychiatrists I know basically only treat adult ADHD cases—they're easy, no long-term maintenance therapy needed!—and it starts to look more like having anxiety is a "disqualifier". What it really means, though, is that the patient will have to get the anxiety under control before a sensible psychiatrist will trust the calibration of the ADHD self-assessment criteria.

It's a muddy situation but your insurance may cover the cost. I explicitly called my insurance provider and asked if they cover the testing required and they said learning disorders weren't covered for adults at all. It was getting to be a big enough issue that I was willing to part with the money out of pocket so I got tested anyways. Insurance ended up paying 100% :/

You will.

Well, true, any information is useful, I guess.