Hi Thomas:
Ultimately, we need to demonstrate that students have learned the material. How that's assessed is as varied as there are topics. My criteria would be that it has to be fair, applicable to all, performed roughly at the same time, uniform in construction, and assess only material that has been covered or assigned (we can't expect students to be mindreaders). If all these criteria are met, then it's only up to the teachers imgination as to best assess learning.
Regards, Barry