Concurrency Test

1import { test } from "node:test";
2import assert from "node:assert/strict";
3import { mapWithConcurrency } from "./concurrency.mjs";
4
5// Regression: audio.mjs used a bare Promise.all(lines.map(synthLine)) to
6// synthesize every TTS line at once, spawning one Kokoro/whisper model load
7// per line concurrently. Two independent reports of this overwhelming a
8// machine (OOM, and cold-start contention causing spurious failures).
9// mapWithConcurrency is the extracted cap; test it in isolation since
10// audio.mjs itself is a script (runs CLI/exit side effects on import).
11test("processes every item and preserves input order regardless of completion order", async () => {
12  const order = [5, 1, 3, 2, 4];
13  const results = await mapWithConcurrency(order, 2, async (n) => {
14    await new Promise((r) => setTimeout(r, n));
15    return n * 10;
16  });
17  assert.deepEqual(results, [50, 10, 30, 20, 40]);
18});
19
20test("never runs more than `limit` at once", async () => {
21  let inFlight = 0;
22  let maxInFlight = 0;
23  const items = Array.from({ length: 10 }, (_, i) => i);
24  await mapWithConcurrency(items, 3, async () => {
25    inFlight++;
26    maxInFlight = Math.max(maxInFlight, inFlight);
27    await new Promise((r) => setTimeout(r, 5));
28    inFlight--;
29  });
30  assert.equal(maxInFlight, 3);
31});
32
33test("limit larger than the item count runs everything without hanging", async () => {
34  const results = await mapWithConcurrency([1, 2], 10, async (n) => n * 2);
35  assert.deepEqual(results, [2, 4]);
36});
37
38test("empty input resolves to an empty array", async () => {
39  const results = await mapWithConcurrency([], 4, async (n) => n);
40  assert.deepEqual(results, []);
41});