A teacher can enable self-enrolment in a course

1. Login as a teacher, access a course and in the course settings allow self-enrolment.
2. Login as a student and enrol in the course.
3. Login as the teacher again and unenrol the student.
4. In the course settings, set an enrolment key.
5. Login as the student again and attempt to enrol in the course.
6. Check that you are required to supply the correct enrolment key before being enrolled in the course.
7. Login as the teacher again and unenrol the student.
8. In the course settings disable self-enrolment.
9. Login as the student again and attempt to enrol in the course.
10. Check that you are no longer allowed to enrol.