Don't sweat it, you don't want to work for the companies that would exclude on such a basis.

I can tell you from my experience being a hiring manager that it's a really tough job. You can see dozens of resumes in a short period (I saw over 100 in a 2 month period), with all degrees of truth and creative fiction. It becomes tempting to try to cull using testing. We used a short technical test. (As an aside, we promised we'd only test for technologies the candidate mentioned on their resume- I was amazed how many people we caught out). I learned slowly that personality "testing" was most effectively done by talking to the candidate, conversational style rather than like an interview. Get them to relax and talk about the things that interest them. Better than a test.

Anyway, I'm with you, pessimism and introversion are not a crutch and are often an asset in the tech profession. That bares out in the experience I've had from the candidates with these traits that became successful team members. I'm an introvert by nature. Introverts are often *better* communicators, because their terror of speaking means they prepare better and are more thoughtful in their responses. Pessimists can also be useful in their defensive approach, just as long as it's not the life draining/buzz killing kind of pessimism that brings everyone down :-)

Don't let other people's attempts to pidgeon hole the "right" candidate get your goat. Ultimately, they'll get what they want and will probably find out that having all the same personalities wasn't what they needed.