public static function register()
    {
        self::$root = null;
        if (true === self::$registered) {
            return;
        }

        if (@stream_wrapper_register(vfsStream::SCHEME, __CLASS__) === false) {
            throw new vfsStreamException('A handler has already been registered for the ' . vfsStream::SCHEME . ' protocol.');
        }

        self::$registered = true;
    }