[Phpmyadmin-devel] Any special reason that "require" but not "require _once" on libraries/common.inc.php

Hi all, I make pull request about adding Unit test case for libraries/ServerStatusData.class.php https://github.com/phpmyadmin/phpmyadmin/pull/394 but a build error if I don't change the "require" to "require _once" on libraries/common.inc.php https://travis-ci.org/phpmyadmin/phpmyadmin/jobs/7221724 it is: Fatal error: Cannot redeclare class PMA_Error_Handler in /home/travis/build/phpmyadmin/phpmyadmin/libraries/Error_Handler.class.php on line 20 I want to know that Any special reason that "require" but not "require _once" on libraries/common.inc.php thanks, Adam