The "strict" option which is in mediawiki's suite.xml is deprecated in phpunit 4.5.0. It appears to be replaced with some more "granular options".
https://github.com/sebastianbergmann/phpunit-documentation/issues/282
https://github.com/sebastianbergmann/phpunit/issues/914
I suppose as long as we support older versions of phpunit, then we should keep strict for now? at some point we should decide which of these other options we want and add them.