Do you see some value in a CodeRunner extension in which students are required to add in a small number of test cases, prior to their adding in their own code? Obviously, the students' test cases would be assessed by running them against the teacher's answer....
This might help embed the value of test driven design, and force students to read the specifications prior to coding.
Sorry if you've already thought about this idea! Just a mad thought.
CodeRunner continues to be very useful to us in Edinburgh, with expanding use.