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testland/sinon-fake-timers-js

Wraps Sinon's standalone @sinonjs/fake-timers library for JS/TS testing: install(), tick() / tickAsync(), setSystemTime(), restore(); covers timers (setTimeout / setInterval / requestAnimationFrame), Date / performance.now() / hrtime, and the toFake option for selective override. Runner-agnostic - drives the clock directly in Mocha, AVA, Jasmine, node:test, or the browser. Use when JS/TS code needs deterministic timer or clock control and the test runner does not already expose this library behind its own built-in fake-timer API.

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advanced-scenarios.mdreferences/

sinon fake-timers advanced scenarios

Selective override, absolute clock jumps, and DST/timezone setup extracted from the core skill. Install / tick / tickAsync / teardown usage stays in SKILL.md.

Selectively fake

const clock = FakeTimers.install({
  now: new Date('2026-05-20T14:30:00Z').getTime(),
  toFake: ['setTimeout', 'setInterval', 'Date'],  // not 'performance', 'hrtime'
});

Useful when you want real performance.now() for benchmarking but fake Date.

setSystemTime

clock.setSystemTime(new Date('2027-01-01T00:00:00Z'));
expect(new Date().toISOString()).toBe('2027-01-01T00:00:00.000Z');

Jumps the clock without ticking any in-flight timers.

DST tests

@sinonjs/fake-timers fakes UTC time; for local-zone DST behaviour, set process.env.TZ first, then install at the UTC instant of the transition.

process.env.TZ = 'America/New_York';
const clock = FakeTimers.install({
  now: new Date('2026-03-08T06:30:00Z').getTime(),  // 02:30 EDT - invalid local
});
// ... test that scheduling at 02:30 local degrades gracefully

The test verifies behaviour at the transition (see the dst-transition-reference skill); the fake clock makes it reproducible.

references

advanced-scenarios.md

SKILL.md

tile.json