def setUp(self):
            policy = asyncio.get_event_loop_policy()
            self.loop = policy.new_event_loop()
            self.set_event_loop(self.loop)

            watcher = self.Watcher()
            watcher.attach_loop(self.loop)
            policy.set_child_watcher(watcher)
            self.addCleanup(policy.set_child_watcher, None)