/**
  * @covers WPSEO_Sitemaps::get_last_modified
  */
 public function test_get_last_modified()
 {
     // create and go to post
     $post_id = $this->factory->post->create();
     $this->go_to(get_permalink($post_id));
     $date = self::$class_instance->get_last_modified(array('post'));
     $post = get_post($post_id);
     $this->assertEquals($date, date('c', strtotime($post->post_modified_gmt)));
 }