test_tool_retry_constant_backoff() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_tool_retry.py lines 591–633

def test_tool_retry_constant_backoff() -> None:
    """Test ToolRetryMiddlewarewith constant backoff (backoff_factor=0)."""
    temp_fail = TemporaryFailureTool(fail_count=2)

    @tool
    def temp_failing_tool(value: str) -> str:
        """Tool that fails temporarily."""
        return temp_fail(value)

    model = FakeToolCallingModel(
        tool_calls=[
            [ToolCall(name="temp_failing_tool", args={"value": "test"}, id="1")],
            [],
        ]
    )

    retry = ToolRetryMiddleware(
        max_retries=2,
        initial_delay=0.1,
        backoff_factor=0.0,  # Constant backoff
        jitter=False,
    )

    agent = create_agent(
        model=model,
        tools=[temp_failing_tool],
        middleware=[retry],
        checkpointer=InMemorySaver(),
    )

    start_time = time.time()
    result = agent.invoke(
        {"messages": [HumanMessage("Use temp failing tool")]},
        {"configurable": {"thread_id": "test"}},
    )
    elapsed = time.time() - start_time

    tool_messages = [m for m in result["messages"] if isinstance(m, ToolMessage)]
    assert len(tool_messages) == 1

    # Expected delays: 0.1 + 0.1 = 0.2 seconds (constant)
    assert elapsed >= 0.15, f"Expected at least 0.15s, got {elapsed}s"
    assert elapsed < 0.5, f"Expected less than 0.5s (exponential would be longer), got {elapsed}s"