test_prefix_response() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_wrap_model_call.py lines 321–344

    def test_prefix_response(self) -> None:
        """Test middleware that adds prefix to response."""

        class PrefixMiddleware(AgentMiddleware):
            def __init__(self, prefix: str):
                super().__init__()
                self.prefix = prefix

            def wrap_model_call(
                self,
                request: ModelRequest,
                handler: Callable[[ModelRequest], ModelResponse],
            ) -> ModelCallResult:
                result = handler(request)
                # result is ModelResponse, extract AIMessage from it
                ai_message = result.result[0]
                return AIMessage(content=f"{self.prefix}{ai_message.content}")

        model = GenericFakeChatModel(messages=iter([AIMessage(content="Response")]))
        agent = create_agent(model=model, middleware=[PrefixMiddleware(prefix="[BOT]: ")])

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

        assert result["messages"][1].content == "[BOT]: Response"