/**
  * @covers WPSEO_Sitemaps::canonical
  */
 public function test_canonical()
 {
     $url = site_url();
     $this->assertNotEmpty(self::$class_instance->canonical($url));
     set_query_var('sitemap', 'sitemap_value');
     $this->assertFalse(self::$class_instance->canonical($url));
     set_query_var('xsl', 'xsl_value');
     $this->assertFalse(self::$class_instance->canonical($url));
 }