test_access_state_in_middleware() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_wrap_model_call.py lines 607–632

    def test_access_state_in_middleware(self) -> None:
        """Test middleware can read and use state."""
        state_values = []

        class StateAwareMiddleware(AgentMiddleware):
            def wrap_model_call(
                self,
                request: ModelRequest,
                handler: Callable[[ModelRequest], ModelResponse],
            ) -> ModelCallResult:
                # Access state from request
                state_values.append(
                    {
                        "messages_count": len(request.state.get("messages", [])),
                    }
                )
                return handler(request)

        model = GenericFakeChatModel(messages=iter([AIMessage(content="Response")]))
        agent = create_agent(model=model, middleware=[StateAwareMiddleware()])

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

        assert len(state_values) == 1
        assert state_values[0]["messages_count"] == 1  # Just The HumanMessage
        assert result["messages"][1].content == "Response"