I don't think I know of any other profession where they make experienced professionals work for free to prove they can do the job before they hire them. This is what it is; it's unpaid, on-spec writing. Any writer in any other writing field will tell you you should never write on spec. But for technical writers, it's expected. (And if I had the $35/hr I usually charge for suchlike freelance assignments for each of these writing tests I've done in the past 2.5 years, I wouldn't be in the financial predicament I'm in now, let me tell you.)
And to be honest, I hate it. I have a portfolio. I have references. I even have a damn website. I can do an in-person interview and talk about how to approach a technical writing problem (which, in, say, scriptwriting, is called a "pitch," and is SOP). What the hell else more do you really need?
Seriously, this is bullshit, and reflects some kind of serious and problematic anxiety on the part of employers. Interviews are way more rigorous than when I started out. It's now expected to do two interviews, sometimes three or as many as four. Plus you're expected to have a comprehensive portfolio and do a writing test. This is crap, and sometimes terminally expensive on an unemployed person's budget.
To the tech world: Get your act together, people. Making people jump through a million hoops *and* do unpaid labour for you is actually not a reasonable position to take, and it's about time the tech field stopped kicking tech writers in the ass this way.
As far as I know, you don't do this to testers, or devs, or even marketing people and graphic designers. Why? Because apparently you respect them more than you respect technical writers. We're professionals too.
Side Note: Incidentally, I have not gotten any of the jobs I've been in consideration for, because I keep being No.2 in the queue.