protected function registerDefaultSubjects()
    {
        $this->registerSubject(self::ADD_DIR, new Subject\AddDirectory($this));
        $this->registerSubject(self::ADD_FILE, new Subject\AddFile($this));
        $this->registerSubject(self::ADD_STRING, new Subject\AddString($this));
        $this->registerSubject(self::BUILD_DIR, new Subject\BuildDirectory($this));
        $this->registerSubject(self::BUILD_ITERATOR, new Subject\BuildIterator($this));
        $this->registerSubject(self::SET_STUB, new Subject\SetStub($this));
    }