test_middleware_can_update_via_system_message_object() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/test_system_message.py lines 404–449

    def test_middleware_can_update_via_system_message_object(self) -> None:
        """Test middleware updating system message using SystemMessage objects."""

        def append_with_metadata_middleware(
            request: ModelRequest,
            handler: Callable[[ModelRequest], ModelResponse],
        ) -> ModelResponse:
            """Append using SystemMessage to preserve metadata."""
            base_content = request.system_message.text if request.system_message else ""
            base_kwargs = request.system_message.additional_kwargs if request.system_message else {}

            new_message = SystemMessage(
                content=base_content + " Additional instructions.",
                additional_kwargs={**base_kwargs, "middleware": "applied"},
            )
            new_request = request.override(system_message=new_message)
            return handler(new_request)

        model = GenericFakeChatModel(messages=iter([AIMessage(content="response")]))
        request = ModelRequest(
            model=model,
            system_message=SystemMessage(
                content="Base prompt", additional_kwargs={"base": "value"}
            ),
            messages=[],
            tool_choice=None,
            tools=[],
            response_format=None,
            state=AgentState(messages=[]),
            runtime=Runtime(),
        )

        captured_request = None

        def mock_handler(req: ModelRequest) -> ModelResponse:
            nonlocal captured_request
            captured_request = req
            return ModelResponse(result=[AIMessage(content="response")])

        append_with_metadata_middleware(request, mock_handler)

        assert captured_request is not None
        assert captured_request.system_message is not None
        assert captured_request.system_message.text == "Base prompt Additional instructions."
        assert captured_request.system_message.additional_kwargs["base"] == "value"
        assert captured_request.system_message.additional_kwargs["middleware"] == "applied"