There was coderunner plugin installed on our system which creates some question categories. Because of which the following PHPUnit tests were failing assertion. 

core\questionlib_test::test_question_categorylist
Failed asserting that two arrays are equal.
— Expected
+++ Actual
@@ @@
Array (

•    0 => '1'
•    1 => 127000
•    2 => 127003
•    3 => 127001
•    4 => 127002
•    5 => 127004
  +    0 => 1
  +    1 => 2
  +    2 => 127000
  +    3 => 127003
  +    4 => 127001
  +    5 => 127002
  +    6 => 127004
  )
   
  /var/www/html/lib/tests/questionlib_test.php:2036
  /var/www/html/lib/phpunit/classes/advanced_testcase.php:81

 
2. test_question_categorylist_bad_data
Error: core\questionlib_test::test_question_categorylist_bad_data
Failed asserting that two arrays are equal.
— Expected
+++ Actual
@@ @@
Array (

•    0 => '1'
•    1 => 127000
•    2 => 127001
•    3 => 127002
  +    0 => 1
  +    1 => 2
  +    2 => 127000
  +    3 => 127001
  +    4 => 127002
  )
   
  /var/www/html/lib/tests/questionlib_test.php:2069
  /var/www/html/lib/phpunit/classes/advanced_testcase.php:81