https://gerrit.wikimedia.org/r/#/c/393783/ tests pass for the extension normally
With https://gerrit.wikimedia.org/r/#/c/393704/
16:10:06 There was 1 failure:
16:10:06
16:10:06 1) Babel\Tests\BabelTest::testRenderPlain
16:10:06 Failed asserting that two strings are identical.
16:10:06 --- Expected
16:10:06 +++ Actual
16:10:06 @@ @@
16:10:06 -<div class="mw-babel-box mw-babel-box-N" dir="ltr">
16:10:06 -{|style=" padding: (babel-cellpadding); border-spacing: (babel-cellspacing);"
16:10:06 -! dir="ltr" | [[(babel-portal: en)|en]]<span class="mw-babel-box-level-N">-N</span>
16:10:06 -| dir="ltr" lang="en" | This user has a [[:Category:en-N|native]] understanding of [[:Category:en|English]].
16:10:06 -|}
16:10:06 -</div>[[Category:en|N]][[Category:en-N]]
16:10:06 +
16:10:06
16:10:06 /home/jenkins/workspace/mediawiki-extensions-hhvm-jessie/src/extensions/Babel/tests/phpunit/BabelTest.php:118
16:10:06 /home/jenkins/workspace/mediawiki-extensions-hhvm-jessie/src/tests/phpunit/MediaWikiTestCase.php:156
16:10:06REL1_27 Babel has no hook for unit tests stuff...
There's numerous changes that landed into REL1_28, but not sure if/what is worth cherry picking. Or, if we don't bother cherry picking that core patch
https://github.com/wikimedia/mediawiki-extensions-Babel/blame/REL1_27/tests/phpunit/BabelTest.php
https://github.com/wikimedia/mediawiki-extensions-Babel/blame/REL1_28/tests/phpunit/BabelTest.php