How to use the djangochannelsrestframework.mixins.RetrieveModelMixin function in djangochannelsrestframework

async def test_retrieve_mixin_consumer():

    class UserSerializer(serializers.ModelSerializer):
        class Meta:
            model = get_user_model()
            fields = ('id', 'username', 'email',)

    class AConsumer(RetrieveModelMixin, GenericAsyncAPIConsumer):
        queryset = get_user_model().objects.all()
        serializer_class = UserSerializer

    assert not get_user_model().objects.all().exists()

    # Test a normal connection
    communicator = WebsocketCommunicator(AConsumer, "/testws/")
    connected, _ = await communicator.connect()
    assert connected

    await communicator.send_json_to(
        {
            "action": "retrieve",
            "pk": 100,
            "request_id": 1
        }

for base in bases:
                for attr_name in dir(base):
                    attr = getattr(base, attr_name)
                    if isinstance(attr, _GenericModelObserver):
                        body[attr_name] = attr.bind_to_model(model_cls=queryset.model)

        return super().__new__(mcs, name, bases, body)


class ObserverConsumerMixin(metaclass=ObserverAPIConsumerMetaclass):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.subscribed_requests = {}  # type: Dict[function, str]


class ObserverModelInstanceMixin(ObserverConsumerMixin, RetrieveModelMixin):
    @action()
    async def subscribe_instance(self, request_id=None, **kwargs):
        if request_id is None:
            raise ValueError("request_id must have a value set")
        # subscribe!
        instance = await database_sync_to_async(self.get_object)(**kwargs)
        await self.handle_instance_change.subscribe(instance=instance)
        self.subscribed_requests[self.__class__.handle_instance_change] = request_id

        return None, status.HTTP_201_CREATED

    @action()
    async def unsubscribe_instance(self, request_id=None, **kwargs):
        if request_id is None:
            raise ValueError("request_id must have a value set")
        # subscribe!