code: def add_result(self, result):
          
          for handler in self._handlers:
              handler(result)
          if self._successful and result.status not in _successful_results:
              self._successful = False
docs: Add an already-constructed :class:`~.TestResult` to this
          :class:`~.ResultCollector`.
  
          This may be used when collecting results created by other
          ResultCollectors (e.g. in subprocesses).