While debugging a phpunit test failure, I noticed that mw-debug-cli.log contains hundreds of kilobytes of this repeated message:
[GlobalTitleFail] RequestContext::getTitle called by ApiDocumentationTest->checkMessage/ApiBase::makeMessage/Message->setContext/DerivativeContext->getTitle/RequestContext->getTitle with no title set
Example: https://integration.wikimedia.org/ci/job/mwext-testextension-php55/8/artifact/log/mw-debug-cli.log