The last 7 or 8 bikes I've bought over the last several years from shops I didn't test ride. I honestly don't think a short test ride is going to tell you much.
What I have participated in is demo days...those are pretty fun and you get a small feel for what a bike is like. I try to go to all the mtb demo days I can get to when the local shops have them. If anything, I get to spend the day riding a bike that I didn't pay for.