I think the most important thing to test is that with this change, computing stats for the question bank still works. So, copied from part of the MDL-78580 tests Real-world tests If you have a large enough quiz enough attempts that the statistics calculation takes a significant length of time, you can do a more realistic test. If you don't have one you can set one up with the following steps, which resulted in a 30 second calculation process on my machine, although it takes a long time to generate the data. Set up Go to Site Administration > Development > Make test course. Create an L-size course (this takes a while). Restore the attached 10-question-quiz.mbz to the course and make a note of the cmid. Place the attached test_big_stats_calc.php in the root of your moodle codebase, and run `php test_big_stats_calc.php --quizcmid= cmid --attempts=10000`. This will generate 10000 attempts at the quiz. This takes a long time. You may want to create a snapshot of your database at this point so you can roll back to re-run the tests. You can also re-attempt the quiz as any student before each test scenario to trigger the recalculation. Test 1 - Question bank If needed, reset the database or re-attempt the quiz. Navigate to the quiz Go to the "Question bank" tab. The page should load immediately, and show an empty or N/A result in the "Needs checking?", "Facility index" and "Discriminative efficiency" statistics columns. In the terminal run `php admin/cli/adhoc_task.php "--execute=\quiz_statistics\task\recalculate"` Wait until you see the message for your quiz, "'...re-calculating statistics for xxx attempts". Reload the Question bank page. The page should load immediately, and show an empty or N/A result in the statistics columns. Wait for the scheduled task to complete. Reload the Question bank page. The page should load immediately, and show 0.00% in the "Facility index" column. If you've used a real quiz with actual answers in the attempts, you may see some real statistics here instead.