Test steps;
1. As a teacher, create an assignment.
2. Set "Blind marking" to "Yes"; leave all other settings as default and save the assignment.
3. Log in as a student and submit the assignment.
4. Log back in as a teacher and in the Assignment settings, verify that you can't change "Blind marking" back to "No"
4. Click "View all submissions"
5. Verify that students' names have been replaced by "Participant" with a randomly generated number
6. Grade the submission and in the Assignment administration block, click "Reveal student identities"
7. Verify that you can now see the identity of the student whose work you graded and that the grade has gone to the gradebook.