/**
  * @covers WPSEO_Twitter::twitter_url
  */
 public function test_twitter_url()
 {
     // create and go to post
     $post_id = $this->factory->post->create();
     $this->go_to(get_permalink($post_id));
     $expected = $this->metatag('url', esc_url(self::$class_instance->canonical(false)));
     self::$class_instance->twitter_url();
     $this->expectOutput($expected);
 }