Fatal error when PHPUnit is not installed
PHPUnit and vfs(stream) are no longer included with the FLOW3 distribution.
But still, the core relies on those libraries.
Running FLOW3 without the respective PEAR packages installed, PHP dies with a fatal error:
Fatal error: require_once() [function.require]: Failed opening required 'PHPUnit/Autoload.php'
IIRC the plan is to get rid of the dependency (as long as you don't want to run the unit tests of course).
But anyways, the fatal error should be avoided by checking for the existence of the required PEAR packages IMO