From a commment on MDL-75576:

... this seems to be causing random PHPUnit test failures in Oracle.

• core_question\local\statistics\statistics_bulk_loader_test::test_load_question_discriminative_efficiency 

  1) core_question\local\statistics\statistics_bulk_loader_test::test_load_question_discriminative_efficiency with data set "Discriminative efficiency" (array(array(array('frog'), array('false'), array('false'), array('false')), array(array('frog'), array('frog'), array('false'), array('false')), array(array('frog'), array('false'), array('frog'), array('false')), array(array('frog'), array('frog'), array('frog'), array('frog'))), array(null, 33.33, 33.33, 100.0), array(array(array('frog'), array('frog'), array('frog'), array('frog')), array(array('false'), array('false'), array('false'), array('false')), array(array('frog'), array('false'), array('false'), array('frog')), array(array('false'), array('frog'), array('frog'), array('false'))), array(50.0, 50.0, 50.0, 50.0), array(50.0, 41.67, 41.67, 75.0))

  Failed asserting that null matches expected 50.0.

  /var/www/html/question/tests/local/statistics/statistics_bulk_loader_test.php:439

  /var/www/html/lib/phpunit/classes/advanced_testcase.php:80

• qbank_statistics\helper_test::test_load_question_discrimination_index 

  1) qbank_statistics\helper_test::test_load_question_discrimination_index with data set "Discrimination Index" (array(array(array('frog'), array('false'), array('false'), array('false')), array(array('frog'), array('frog'), array('false'), array('false')), array(array('frog'), array('false'), array('frog'), array('false')), array(array('frog'), array('frog'), array('frog'), array('frog'))), array('N/A', '30.15%', '30.15%', '81.65%'), array(array(array('frog'), array('frog'), array('frog'), array('frog')), array(array('false'), array('false'), array('false'), array('false')), array(array('frog'), array('false'), array('false'), array('frog')), array(array('false'), array('frog'), array('frog'), array('false'))), array('44.72%', '44.72%', '44.72%', '44.72%'), array('44.72%', '37.44%', '37.44%', '63.19%'))

  Failure in quiz 1 - question 2 discrimination index

  Failed asserting that two strings are equal.

  — Expected

  +++ Actual

  @@ @@

  -'30.15%'

  +'N/A'

  /var/www/html/question/bank/statistics/tests/helper_test.php:522

  /var/www/html/lib/phpunit/classes/advanced_testcase.php:80

• qbank_statistics\helper_test::test_load_question_facility 

  1) qbank_statistics\helper_test::test_load_question_facility with data set "Facility case 1" (array(array(array('frog'), array('false'), array('false'), array('false'))), array('100.00%', '0.00%', '0.00%', '0.00%'), array(array(array('frog'), array('false'), array('false'), array('false')), array(array('frog'), array('frog'), array('false'), array('false'))), array('100.00%', '50.00%', '0.00%', '0.00%'), array('100.00%', '25.00%', '0.00%', '0.00%'))

  Failed asserting that two strings are equal.

  — Expected

  +++ Actual

  @@ @@

  -'100.00%'

  +'N/A'

  /var/www/html/question/bank/statistics/tests/helper_test.php:329

  /var/www/html/lib/phpunit/classes/advanced_testcase.php:80