Feature: allow for user defined test cases

Could we implement a feature where students must create a number of expected inputs and outputs for a given a problem in order to "pass" it?

Testing code is a core competency of the course but all we have are mutation testing, which is a pretty advanced topic. Can we make it simpler and just ask students to create lists of I/O? Maybe this should be a problem category on its own, and not added to all code-writing problems. Maybe we just have a number of problems that have the solution implemented and ask students to write simple test cases (not trying to catch bugs like mutation testing)