tests/test_parallel.py

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import time

import pytest

from ntfc.parallel import run_parallel


def test_run_parallel_empty_returns_empty_list() -> None:
    assert run_parallel([], lambda item: item) == []


def test_run_parallel_preserves_input_order() -> None:
    items = [1, 2, 3]

    def worker(item: int) -> int:
        # Delay inversely to item value to force out-of-order completion.
        time.sleep((4 - item) * 0.01)
        return item * 10

    assert run_parallel(items, worker) == [10, 20, 30]


def test_run_parallel_propagates_worker_exception() -> None:
    def worker(item: int) -> int:
        if item == 2:
            raise ValueError("boom")
        return item

    with pytest.raises(ValueError, match="boom"):
        run_parallel([1, 2, 3], worker)