code: def _common_setup(self):
          
          self._started = True
          self._reactor = self._reactorFactory()
          self._registry = ResultRegistry()
          # We want to unblock EventualResult regardless of how the reactor is
          # run, so we always register this:
          self._reactor.addSystemEventTrigger(
              "before", "shutdown", self._registry.stop)
docs: The minimal amount of setup done by both setup() and no_setup().