For me, the most "open" a test was, the more I worried about it. Expecting students to remember everything on the test meant that it had to be easy.
The hardest exam I ever took was my final exam for Linear Algebra. It was so "open" that people could use matlab on a shared computer that was also projected to the entire class. Turns out, the best students in the class didn't need help on a computer, so it turned into this kind of mind-fuck where you weren't sure if they got a different answer than you because they were wrong, or because you were. To add to the excitement, the questions all tied together and used the answer from the previous one, so if you missed one, you were guaranteed to miss every subsequent question.
The hardest exam I ever took was my final exam for Linear Algebra. It was so "open" that people could use matlab on a shared computer that was also projected to the entire class. Turns out, the best students in the class didn't need help on a computer, so it turned into this kind of mind-fuck where you weren't sure if they got a different answer than you because they were wrong, or because you were. To add to the excitement, the questions all tied together and used the answer from the previous one, so if you missed one, you were guaranteed to miss every subsequent question.