How to use the pykka.ActorRegistry.unregister function in pykka

def test_actor_may_be_unregistered_multiple_times_without_error(actor_ref):
    ActorRegistry.unregister(actor_ref)
    assert actor_ref not in ActorRegistry.get_all()

    ActorRegistry.unregister(actor_ref)
    assert actor_ref not in ActorRegistry.get_all()

    ActorRegistry.register(actor_ref)
    assert actor_ref in ActorRegistry.get_all()

def test_actor_may_be_registered_manually(actor_ref):
    ActorRegistry.unregister(actor_ref)
    assert actor_ref not in ActorRegistry.get_all()

    ActorRegistry.register(actor_ref)

    assert actor_ref in ActorRegistry.get_all()

def _handle_failure(self, exception_type, exception_value, traceback):
        """Logs unexpected failures, unregisters and stops the actor."""
        logger.error(
            'Unhandled exception in {}:'.format(self),
            exc_info=(exception_type, exception_value, traceback),
        )
        ActorRegistry.unregister(self.actor_ref)
        self.actor_stopped.set()

def stop(self):
        if self.bookmarks:
            logger.debug('Stopping %s', self.bookmarks)
            try:
                self.bookmarks.stop(timeout=1)
            except pykka.Timeout:
                # bookmarks actor may be waiting on backend
                pykka.ActorRegistry.unregister(self.bookmarks)