test_summarization_middleware_trim_messages_error_fallback() — langchain Function Reference

Source Code

libs/langchain_v1/tests/unit_tests/agents/middleware/implementations/test_summarization.py lines 735–750

def test_summarization_middleware_trim_messages_error_fallback() -> None:
    """Test that trim_messages_for_summary falls back gracefully on errors."""
    middleware = SummarizationMiddleware(model=MockChatModel(), trigger=("messages", 5))

    # Create a mock token counter that raises an exception
    def failing_token_counter(_: Iterable[MessageLikeRepresentation]) -> int:
        msg = "Token counting failed"
        raise ValueError(msg)

    middleware.token_counter = failing_token_counter

    # Should fall back to last 15 messages
    messages: list[AnyMessage] = [HumanMessage(content=str(i)) for i in range(20)]
    trimmed = middleware._trim_messages_for_summary(messages)
    assert len(trimmed) == 15
    assert trimmed == messages[-15:]