Personally, I hate tests. HATE them. As a kid I was a terrible test taker and it never got much better as I got older. I still wonder how I managed to graduate college with a 4.0. The term "sliding scale" comes to mind.
The ability to consume and regurgitate facts on the spot is sure to make mom proud when you come home with an "A", but outside academia, does anyone care? My dad still calls me "Suma" (short for Suma Cum Laude) but beyond that, all that effort in college boiled down to some bragging rights and a line on my resume.
In my opinion you can't test for the things that really matter in a web development agency partner. Is there some way to test if a company is going to provide tangible value and long term return on investment on a project? Is there a way to tell if a company is going to solve the underlying business problem or simply use technology to solve one problem and create three more new ones in the process? Not really. All customers have to go on is a company's track record and client list, and even that can be skewed. Reputation and genuine customer referrals are the real test in my opinion.
I've known for years that my business partner, Bonify's CTO, Dan Pepin, is one of the best Drupal developers out there, and so have our customers. When it was recently suggested that Bonify go for the Acquia Drupal Certification I initially met the idea with resistance, as a non-believer in tests. I'd rather we be judged on the merits of our work as a team and the results we produce, but in the end we decided to go for it anyway. Not because it matters to us, but because it may matter to prospective customers as something they can believe in. Perhaps they'll sleep better knowing that their vendor of choice has a certified project lead.
So today we decided on a lark to go for it. No studying. Dan got 90% going in cold. Mom would be proud.
The Drupal community calls the test very hard and difficult to study for. Sounds an awful lot like delivering great sites with high ROI. Very hard and difficult to study for.