code: def assert_no_404_errors(self, multithreaded=True):
          
          links = self.get_unique_links()
          if multithreaded:
              from multiprocessing.dummy import Pool as ThreadPool
              pool = ThreadPool(10)
              pool.map(self.assert_link_status_code_is_not_404, links)
              pool.close()
              pool.join()
          else:
              for link in links:
                  self.assert_link_status_code_is_not_404(link)
docs: Assert no 404 errors from page links obtained from:
              "a"->"href", "img"->"src", "link"->"href", and "script"->"src".