docs: def heartbeat(self):
          """
          Watch our counters--as long as things are incrementing, send a ping to
          statuscake sayin we are alive and okay.
          """
  
          self.thread_debug("heartbeat")
  
          # check stats -- should be incrementing
          if self.last_stats:
              if self.stats.http_run <= self.last_stats.http_run:
                  self.NOTIFY("No monitors run since last heartbeat!", service="heartbeat")
                  return
              elif self.stats.http_handled <= self.last_stats.http_handled:
                  self.NOTIFY("No monitor results handled since last heartbeat!", service="heartbeat")
                  return
  
          # ping heartbeat as a webhook
          if self.config.get('heartbeat-hook'):
              result = requests.get(self.config.get('heartbeat-hook'))
              if result.status_code != 200:
                  self.NOTIFY("Heartbeat ping to statuscake failed!", level="ERROR")
  
          # keep a static copy of the last run stats
          self.last_stats = self.stats.copy()