The particular case that was failing is: 1. Create a quiz with a close date in the future 2. Create a quiz group override with a close date in the past 3. Start an attempt using a student not in the overridden group 4. Run the moodle cron (and ensure update_overdue_attempts() runs). The student's attempt should NOT be closed. You may also wish to test some other cases. For example, create an attempt by a student in the overridden group before the group close date passes, as well, and make sure that is still closed.