The RelatedArticles tests depends on some other repositories. @bmansurov made a change to CI to have the repository tests with a bunch of other repositories (mediawiki-extensions-*) jobs.
An example test report is https://integration.wikimedia.org/ci/job/mediawiki-extensions-hhvm/35991/testReport/ :
EchoTitleLocalCacheTest::testGet mysql_real_escape_string() expects parameter 1 to be string, array given Path: /mnt/jenkins-workspace/workspace/mediawiki-extensions-hhvm/src/ includes/db/DatabaseMysqli.php:309 includes/db/DatabaseMysqlBase.php:560 includes/db/Database.php:2531 includes/db/Database.php:2077 includes/db/Database.php:1914 includes/db/DBConnRef.php:39 includes/db/DBConnRef.php:268 includes/deferred/LinksUpdate.php:343 includes/deferred/LinksUpdate.php:208 includes/deferred/LinksUpdate.php:145 includes/deferred/DataUpdate.php:99 includes/deferred/DeferredUpdates.php:119 includes/deferred/DeferredUpdates.php:79 includes/page/WikiPage.php:2185 includes/page/WikiPage.php:1947 tests/phpunit/MediaWikiTestCase.php:447 extensions/Echo/tests/phpunit/cache/TitleLocalCacheTest.php:28 tests/phpunit/MediaWikiTestCase.php:137
I reproduced it locally with Sqlite and just Echo + RelatedArticles.
For Sqlite that ends up falling when calling addQuotes() on an array. I also spotted some warnings such as:
Warning: bin2hex() expects parameter 1 to be string, array given in includes/db/DatabaseSqlite.php on line 817
What I found is that it seems to be caused by the RelatedArticles hook onParserClearState which does:
$parser->getOutput()->setProperty( 'RelatedArticles', array() );
If I comment it out, it is all fine.
To test the behavior, one can propose a dummy patch in Gerrit for RelatedArticles then comment check experimental. That will run the mediawiki-extensions-hhvm job and inject RelatedArticles into it.