There is something to be said about design tests for designers when one has 10+ or even 20+ years of experience. Is it not just a way of getting to know each other better? 10+ or even 20+ years of experience does not make a designer adequate for any job in any sector right ? Not all designers are the same, we do not all excel at the same things. While some can thrive for 20 years in some environments it could be possible that they would seriously underperform in others.. I have had interviews with designers that were doing well for themselves, with interesting resumes, but that weren't a match for our environment and the specific role. That became more apparent as we discussed some case studies. Not a long drawn out "design test" but just presenting them with real life design cases from our company and hearing their thoughts on it. Vice-versa a candidate may realise they do not like the subject or environment (or people ;) ) through this kind of "simulation".
Don't know what kind of design test you had to go through, but I imagine it having the same effect. In any case it helped you stay away from a toxic environment. :)