TestWrapModelCallDecorator Class — langchain Architecture

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_wrap_model_call.py lines 1005–1376

class TestWrapModelCallDecorator:
    """Test the @wrap_model_call decorator for creating middleware."""

    def test_basic_decorator_usage(self) -> None:
        """Test basic decorator usage without parameters."""

        @wrap_model_call
        def passthrough_middleware(
            request: ModelRequest,
            handler: Callable[[ModelRequest], ModelResponse],
        ) -> ModelCallResult:
            return handler(request)

        # Should return an AgentMiddleware instance
        assert isinstance(passthrough_middleware, AgentMiddleware)

        # Should work in agent
        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
        agent = create_agent(model=model, middleware=[passthrough_middleware])

        result = agent.invoke({"messages": [HumanMessage("Hi")]})
        assert len(result["messages"]) == 2
        assert result["messages"][1].content == "Hello"

    def test_decorator_with_custom_name(self) -> None:
        """Test decorator with custom middleware name."""

        @wrap_model_call(name="CustomMiddleware")
        def my_middleware(
            request: ModelRequest,
            handler: Callable[[ModelRequest], ModelResponse],
        ) -> ModelCallResult:
            return handler(request)

        assert isinstance(my_middleware, AgentMiddleware)
        assert my_middleware.__class__.__name__ == "CustomMiddleware"

    def test_decorator_retry_logic(self) -> None:
        """Test decorator for implementing retry logic."""
        call_count = {"value": 0}

        class FailOnceThenSucceed(GenericFakeChatModel):
            @override
            def _generate(
                self,
                messages: list[BaseMessage],
                stop: list[str] | None = None,
                run_manager: CallbackManagerForLLMRun | None = None,
                **kwargs: Any,
            ) -> ChatResult:
                call_count["value"] += 1
                if call_count["value"] == 1:
                    msg = "First call fails"
                    raise ValueError(msg)
                return super()._generate(messages, **kwargs)

        @wrap_model_call
        def retry_once(
            request: ModelRequest,
            handler: Callable[[ModelRequest], ModelResponse],
        ) -> ModelCallResult:
            try:
                return handler(request)
            except Exception:
                # Retry once
                return handler(request)

        model = FailOnceThenSucceed(messages=iter([AIMessage(content="Success")]))
        agent = create_agent(model=model, middleware=[retry_once])

        result = agent.invoke({"messages": [HumanMessage("Test")]})

        assert call_count["value"] == 2
        assert result["messages"][1].content == "Success"

    def test_decorator_response_rewriting(self) -> None:
        """Test decorator for rewriting responses."""

        @wrap_model_call
        def uppercase_responses(
            request: ModelRequest,