test_command_messages_added_alongside_model_messages() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_wrap_model_call_state_update.py lines 29–55

    def test_command_messages_added_alongside_model_messages(self) -> None:
        """Command messages are added alongside model response messages (additive)."""

        class AddMessagesMiddleware(AgentMiddleware):
            def wrap_model_call(
                self,
                request: ModelRequest,
                handler: Callable[[ModelRequest], ModelResponse],
            ) -> ExtendedModelResponse:
                response = handler(request)
                custom_msg = HumanMessage(content="Custom message", id="custom")
                return ExtendedModelResponse(
                    model_response=response,
                    command=Command(update={"messages": [custom_msg]}),
                )

        model = GenericFakeChatModel(messages=iter([AIMessage(content="Hello!")]))
        agent = create_agent(model=model, middleware=[AddMessagesMiddleware()])

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

        # Both model response AND command messages appear (additive via add_messages)
        messages = result["messages"]
        assert len(messages) == 3
        assert messages[0].content == "Hi"
        assert messages[1].content == "Hello!"
        assert messages[2].content == "Custom message"