> xdebug_on; php5 /vagrant/mediawiki/tests/phpunit/phpunit.php --wiki=wiki /vagrant/mediawiki/extensions/Extension/tests/phpunit/SomeTest.php; xdebug_off
Yeah, that command doesn't exist. And php5? Really?
Topic on Manual talk:How to debug/Archive 2
xdebug_on and xdebug_off are shell functions included in MediaWiki-Vagrant. They set and clear the environment variables XDEBUG_CONFIG and PHP_IDE_CONFIG. The docs could make this more clear.
The explicit use of php5 is also a dated reference to MediaWiki-Vagrant configuration. Modern MediaWiki-Vagrant usage should be just php or possibly php7.2. The legacy php5 was once needed to select a Zend-based PHP runtime rather than an HHVM runtime.