// test 2 tables with aliases and limits with order bys (limit which is out of range)
$records = $DB->get_records_sql($sql, null, 21098765432109876543210, 2); // Skip all courses
$this->assertEqual(0, count($records));

// test 2 tables with aliases and limits with order bys (limit which is out of range)
$records = $DB->get_records_sql($sql, null, 21098765432109876543210, 21098765432109876543210); // Skip all courses
$this->assertEqual(0, count($records));

these tests are wrong, you can not type large numbers like this in PHP.