Some extension are autoloading php files which contains a die for non-mediawiki environment like it is happen when running "composer test". It is possible for jenkins to take a die of composer test as failure?
I am not sure if that is possible, would be nice if possible but it also okay to wontfix this task.
Example:
https://integration.wikimedia.org/ci/job/mwext-testextension-hhvm-composer-jessie/7250/console
17:05:16 + composer --ansi test 17:05:18 > parallel-lint . --exclude vendor 17:05:18 This version of the BlueSpiceEditNotifyConnector extension requires MediaWiki 1.25+[mwext-testextension-hhvm-composer-jessie] $ /bin/bash -xe /tmp/hudson1773069237167295866.sh 17:05:18 + git -C src/extensions/BlueSpiceEditNotifyConnector clean -xqdf 17:05:18 [mwext-testextension-hhvm-composer-jessie] $ /bin/bash -xe /tmp/hudson1316596872851084922.sh 17:05:18 + /srv/deployment/integration/slave-scripts/bin/mw-run-phpunit-allexts.sh 17:05:18 + cd /home/jenkins/workspace/mwext-testextension-hhvm-composer-jessie/src/tests/phpunit 17:05:18