Run phpunit lib/tests/accesslib_test.php and make sure everything passes. Grep for get_parent_contexts and make sure it's not used in core (except for Unit Tests). Explore and check for regression in the following: Search for users in "Existing role holders" in admin/roles Backup and restore a course Enrolment category Enrolment cohort Enrolment in general (get_total_users, get_other_users) Blocks (add, delete, edit, etc...) Call one Web Service function (the authentication is what you want to test) Grade displayed as a letter