I agree with Val. If the open-book test allows a student access to formulas and such, I'm all for it. IRL, people don't blindly memorize everything. They memorize what they need to use regularly, and they do so because it is useful to them. Everything else they record in books and notes.
Knowing how to solve problems is a very different animal from memorization. Done correctly, an open-book test can be a very successful discriminator (in the best sense of the word) for separating those who really grasp the material from those who do not.
