For this test you will need an assignment with online text enabled.
1) As a student submit the assignment.
2) As a teacher grade the submission and verify that the student's grade appears in the grader report.
3) Turn editing on and override a grade in the grader report by clicking it then typing a new grade in the left hand text box and pressing enter.
4) The grade should be updated and the background color of the cell should change to indicate that the grade has been overriden.
5) Return to the assignment and check that you can no longer alter the grade. The grade selector should be disabled and a link to the grader report provided.
6) Go back to the grader report, turn editing on and click the edit icon (hand holding a pencil) for the assignment.
7) Uncheck the overidden checkbox and press save. Turn editing off.
8) Verify that you are returned to the grader report and that it now displays the student's original grade.
9) Return to the assignment and verify that you can now alter the grade.