Testing several Mobile related extensions together ( https://integration.wikimedia.org/ci/job/mediawiki-phpunit-integration-hhvm/4/ ), raised tests not passing:
AutoLoaderTest.testAutoLoadConfig ResourcesTest.testMissingDependencies ResourcesTest.testUnsatisfiableDependencies
They are caught in core via the 'structure' tests available in tests/phpunit/structure.
On MediaWiki extension, we run the testextension-{hhvm,zend} which invokes:
phpunit --testsuite extensions
The extensions suite defined in tests/phpunit/suite.xml should include the structure directory to have those tests run on extensions.