TestRetryLogic Class — langchain Architecture

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/core/test_wrap_model_call.py lines 106–293

class TestRetryLogic:
    """Test retry logic with wrap_model_call."""

    def test_simple_retry_on_error(self) -> None:
        """Test middleware that retries once on error."""
        call_count = {"value": 0}

        class FailOnceThenSucceed(GenericFakeChatModel):
            @override
            def _generate(
                self,
                messages: list[BaseMessage],
                stop: list[str] | None = None,
                run_manager: CallbackManagerForLLMRun | None = None,
                **kwargs: Any,
            ) -> ChatResult:
                call_count["value"] += 1
                if call_count["value"] == 1:
                    msg = "First call fails"
                    raise ValueError(msg)
                return super()._generate(messages, **kwargs)

        class RetryOnceMiddleware(AgentMiddleware):
            def __init__(self) -> None:
                super().__init__()
                self.retry_count = 0

            def wrap_model_call(
                self,
                request: ModelRequest,
                handler: Callable[[ModelRequest], ModelResponse],
            ) -> ModelCallResult:
                try:
                    return handler(request)
                except Exception:
                    self.retry_count += 1
                    return handler(request)

        retry_middleware = RetryOnceMiddleware()
        model = FailOnceThenSucceed(messages=iter([AIMessage(content="Success")]))
        agent = create_agent(model=model, middleware=[retry_middleware])

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

        assert retry_middleware.retry_count == 1
        assert result["messages"][1].content == "Success"

    def test_max_retries(self) -> None:
        """Test middleware with maximum retry limit."""

        class AlwaysFailModel(GenericFakeChatModel):
            @override
            def _generate(
                self,
                messages: list[BaseMessage],
                stop: list[str] | None = None,
                run_manager: CallbackManagerForLLMRun | None = None,
                **kwargs: Any,
            ) -> ChatResult:
                msg = "Always fails"
                raise ValueError(msg)

        class MaxRetriesMiddleware(AgentMiddleware):
            def __init__(self, max_retries: int = 3):
                super().__init__()
                self.max_retries = max_retries
                self.attempts = []

            def wrap_model_call(
                self,
                request: ModelRequest,
                handler: Callable[[ModelRequest], ModelResponse],
            ) -> ModelCallResult:
                last_exception = None
                for attempt in range(self.max_retries):
                    self.attempts.append(attempt + 1)
                    try:
                        return handler(request)
                    except Exception as e:
                        last_exception = e
                        continue