public function testHasChildObject()
 {
     ConcreteArticleQuery::create()->deleteAll();
     ConcreteQuizzQuery::create()->deleteAll();
     ConcreteContentQuery::create()->deleteAll();
     $content = new ConcreteContent();
     $content->save();
     $this->assertFalse($content->hasChildObject());
     $article = new ConcreteArticle();
     $article->save();
     $content = $article->getConcreteContent();
     $this->assertTrue($content->hasChildObject());
 }