test_command_with_custom_state_field() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_wrap_model_call_state_update.py lines 115–142

    def test_command_with_custom_state_field(self) -> None:
        """When command updates a custom field, model response messages are preserved."""

        class CustomFieldMiddleware(AgentMiddleware):
            def wrap_model_call(
                self,
                request: ModelRequest,
                handler: Callable[[ModelRequest], ModelResponse],
            ) -> ExtendedModelResponse:
                response = handler(request)
                return ExtendedModelResponse(
                    model_response=response,
                    command=Command(update={"custom_key": "custom_value"}),
                )

        class CustomState(AgentState):
            custom_key: str

        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello")]))
        agent = create_agent(
            model=model,
            middleware=[CustomFieldMiddleware()],
            state_schema=CustomState,
        )

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

        assert result["messages"][-1].content == "Hello"