# no-misused-concurrency

📝 Disallow the `concurrency` option on a test without subtests.

💼 This rule is enabled in the following [configs](https://github.com/sindresorhus/eslint-node-test#preset-configs): ✅ `recommended`, ☑️ `unopinionated`.

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The `concurrency` option controls how many of a suite's tests, or a test's *subtests*, run at the same time. On a leaf test that has no subtests there is nothing for it to govern, so the option does nothing. It is usually a misunderstanding carried over from Jest or Vitest, where concurrency applies to the test itself.

This rule reports the `concurrency` option on a `test`/`it` (or a subtest) whose callback creates no subtests. Use it on a `describe`/`suite`, or on a test that creates subtests with `t.test()`.

> [!NOTE]
> Only subtests created by an inline `t.test(…)` call in the test callback are detected. A test that creates its subtests indirectly, for example through a helper function it calls, is still reported.

## Examples

```js
import test from 'node:test';

// ❌ — no subtests, so `concurrency` does nothing
test('does work', {concurrency: true}, () => {
	assert.ok(result);
});

// ✅ — governs how the subtests run
test('group', {concurrency: true}, async t => {
	await t.test('a', () => {});
	await t.test('b', () => {});
});
```