List each test result and its count in descending order of count.
SELECT test_result ,  COUNT(*) FROM Student_Tests_Taken GROUP BY test_result ORDER BY COUNT(*) DESC
SELECT test_result ,  COUNT(*) FROM Student_Tests_Taken GROUP BY test_result ORDER BY COUNT(*) DESC
[{'test_result': 'Pass', 'COUNT(*)': 8}, {'test_result': 'Fail', 'COUNT(*)': 7}]