It sounds like you're pretty new to CodeRunner so it's probably best if you put the idea of a JUnit question type on hold until you've had a bit more experience. The prototype I gave you was something I threw together as in a hurry, but it's a rather difficult example and not a good starting point for learning. Furthermore, I just looked at it and saw a silly coding error which would give exactly the output you're getting if the test or program failed to compile. I've replaced the attachment in the the original post with a bug-fixed version, and I attach the updated version to this posting, too. You must delete the existing prototype before importing the new .xml or you'll get a prototype error. However, it's still not going to be useful in its present form, so I don't think it's worth proceeding until you're up to speed with writing templates, template debugging, defining new question types and a heap of other complexities. My apologies for tossing such a demanding exercise at you.
If you really really wish to proceed anyway, you'll need to read all the documentation on writing templates and authoring new question types. The example I gave you uses a combinator template grader, the most difficult type. The error message you're getting suggests that the program isn't generating any output, which is exactly what would happen with the first version I posted if anything went wrong (even a compile error - I had tested handling of compile errors while developing but made a last minute change which broke things).
To debug and develop the question type further (are you sure you want to do this?) you will need to proceed as follows:
- Create an empty directory for testing. Download the two support files from the prototype (hamcrest_core and junit 4.13 beta) into that directory.
- In the test question (calculator, or whatever), turn on the Template debugging checkbox.
- Run the test question (i.e. preview it and click Check).
- Copy the Debug source code from the run (assuming only one run took place) into a file tester.py within the test directory you set up.
- Run tester.py (you'll need python3 installed to run it). The output should be a JSON string containing the mark in an attribute fraction and the test output in an attribute prologuehtml.
- Debug as required.
- Copy the corrections back into the prototype's template, but make sure you don't clobber the Twig code that inserts the student's answer into the template.