test_middleware_modifies_request() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_wrap_model_call.py lines 1538–1558

    def test_middleware_modifies_request(self) -> None:
        """Test middleware that modifies the request before execution."""
        modified_messages = []

        class RequestModifyingMiddleware(AgentMiddleware):
            def wrap_model_call(
                self,
                request: ModelRequest,
                handler: Callable[[ModelRequest], ModelResponse],
            ) -> ModelCallResult:
                # Add a system message to the request
                modified_request = request
                modified_messages.append(len(modified_request.messages))
                return handler(modified_request)

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

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

        assert len(modified_messages) == 1