There is also a lot to learn by sharing, during a workshop, how to finish the challenges. Even if the number of tests might be limited how to get to those tests, how to think them is different form person to person.
Creating new scenarios is also very challenging. You need to know and understand what to test, how to test and to come up with a algorithm that validates or invalidates the inputs and actions. I found that brainstorming within a group is very useful to come up with new ideas to talk about what and how to test it.