In order to get an automatic grading for this question you need to create and implement a JUnit test-file. This file needs to match exactly the class and function names used in the source code written in the "Given code for student" HTML-editor.
The number of your implemented test cases need to match the number in "Default question grade". For each test case the student can get 1 point. If you have for example five test cases in your test-file you should set the "Default question grade" to "5". If the response of the student passes all test cases he/she will get 5 points out of 5. Otherwise each failed test case will subtract 1 point of the possible.
If you haven't uploaded the proper test-file into your current course yet you may do it now. Then choose that file to use it for this question. Make sure your loaded test-file ends with ".java". Another very important point is that your test-file compiles, check this if not done already! You can check this also by previewing your question or Quiz.