PagesList has a sub repo DataTables, which is not known by the test framework and such this gives error when tests are running:
19:46:49 3) Warning 19:46:49 The data provider specified for ResourcesTest::testFileExistence is invalid. 19:46:49 ResourceLoaderFileModule::readStyleFile: style file not found: "/home/jenkins/workspace/mediawiki-extensions-hhvm-jessie/src/extensions/PagesList/modules/DataTables/media/css/jquery.dataTables.css" 19:46:49 19:46:49 /home/jenkins/workspace/mediawiki-extensions-hhvm-jessie/src/maintenance/doMaintenance.php:111
One solution is to bundle the files with the extension, makes install easier. See T154806 for a discussion about this problem on another repo