test_tool_retry_custom_failure_formatter() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_tool_retry.py lines 250–284

def test_tool_retry_custom_failure_formatter() -> None:
    """Test ToolRetryMiddlewarewith custom failure message formatter."""

    def custom_formatter(exc: Exception) -> str:
        return f"Custom error: {type(exc).__name__}"

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

    retry = ToolRetryMiddleware(
        max_retries=1,
        initial_delay=0.01,
        jitter=False,
        on_failure=custom_formatter,
    )

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

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

    tool_messages = [m for m in result["messages"] if isinstance(m, ToolMessage)]
    assert len(tool_messages) == 1
    assert "Custom error: ValueError" in tool_messages[0].content