Tests for maintenance scripts might want to cover some situations that cause the script to fatal. Currently, this isn't possible because Maintenance::fatalError calls exit() and brings the suite down. I think a quick and effective solution might be to create a new error type, MaintenanceFatalError extends \Error. Then the exit() can be replaced with throwing this error, either always (but need to ensure this won't break anything), or only if MW_PHPUNIT_TEST is defined.