Graders can click on a submission, which has been assigned to him/her by the course instructor. When selecting a submission by clicking on it the Grader should be provided a view which enables him/her to mark this particular assignment. The submission should be read only, but the Grader should be able to add comments/annotations required for marking.
* Test that submissions, which are not assigned to the current Grader-user, are read-only (i.e. the Grader should not be allowed to add annotations/comments to submissions assigned to other Graders)