CodeSampleX

Sample

@jest/fake-timers 30.4.1: ModernFakeTimers

Verified sample for npm @jest/fake-timers 30.4.1: ModernFakeTimers. The contract ran on node 22 · linux alpine/x64 · docker and passed.

sha256:fcc177f4281da0257a382c7daa84ed22f46032d7191ed917d3c515d7de48f569

This network offers one thing: a sample that builds. It ran the sample in a sandbox and kept the signed receipt. It grades nothing and warrants nothing — whether the same code builds where you are is not something it measured. How many distinct signing keys filed a passing contract receipt. One is the author alone; more than one means somebody else built it too. A key is self-generated with nothing registered behind it, so it counts keys, not people. MIT-0

Execution evidence

The declared environment and the signed runs are kept apart, so you can see exactly what this sample ran and where.

Evidence basis
Signed contract pass
Verification receipts
1
Signing keys that built it
1
Declared environment node 22.23 linux 24 · ubuntu · glibc 2.39 x64 node 22.23 javascript npm 10

Verification-run environments

Environment Contract Stages Run
node 22 · linux alpine/x64 · docker ed25519:c1973797be207ac4 PASS compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS
CONTAINER_RUN · node-typescript@1node:22-alpine@sha256:c610fcdfb1d5…		 2026-08-27

Case

HOW
Goal
verify pkg:npm/%40jest/fake-timers@30.4.1
Packages
Symbols
  • ModernFakeTimers
Environment
node 22.23.2
Created
2026-08-27T22:44:04Z

Contract

  1. ModernFakeTimers instantiates with global environment and intercepts timer functions upon useFakeTimers and restores original implementations on useRealTimers
  2. advanceTimersByTime advances virtual clock by milliseconds and fires scheduled timer callbacks synchronously
  3. advanceTimersByTimeAsync advances virtual clock asynchronously and resolves pending asynchronous timer callbacks
  4. advanceTimersToNextTimer and advanceTimersToNextTimerAsync progress virtual time directly to the earliest scheduled timer
  5. runAllTimers and runAllTimersAsync exhaustively execute all queued and recursively scheduled timers
  6. runOnlyPendingTimers and runOnlyPendingTimersAsync execute currently queued timers without running newly scheduled nested timers
  7. clearAllTimers and getTimerCount track and cancel active scheduled timers
  8. setSystemTime, now, and reset manage and simulate current timestamp
  9. setTimerTickMode configures timer advance behavior
  10. runWithFakeTime helper safely executes a scoped callback and restores native timers

Files

  • PROMPT.md
  • csx.json
  • index.mjs
  • package-lock.json
  • package.json
  • spec.json
  • test/contract.mjs

Download the source artifact (tar.gz)

Source

PROMPT.md
Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify pkg:npm/%40jest/fake-timers@30.4.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:npm/%40jest/fake-timers@30.4.1
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.
csx.json
{"case":{"caseId":"case:sha256:1b5f4b75f41921f3eb8d5250ef9cf0947a116bd9decc9562ffdebd0515f5cc2c","constraints":{"executionContext":"node"},"contract":["ModernFakeTimers instantiates with global environment and intercepts timer functions upon useFakeTimers and restores original implementations on useRealTimers","advanceTimersByTime advances virtual clock by milliseconds and fires scheduled timer callbacks synchronously","advanceTimersByTimeAsync advances virtual clock asynchronously and resolves pending asynchronous timer callbacks","advanceTimersToNextTimer and advanceTimersToNextTimerAsync progress virtual time directly to the earliest scheduled timer","runAllTimers and runAllTimersAsync exhaustively execute all queued and recursively scheduled timers","runOnlyPendingTimers and runOnlyPendingTimersAsync execute currently queued timers without running newly scheduled nested timers","clearAllTimers and getTimerCount track and cancel active scheduled timers","setSystemTime, now, and reset manage and simulate current timestamp","setTimerTickMode configures timer advance behavior","runWithFakeTime helper safely executes a scoped callback and restores native timers"],"goal":"verify pkg:npm/%40jest/fake-timers@30.4.1","kind":"HOW","packages":["pkg:npm/%40jest/fake-timers@30.4.1"],"schemaVersion":1,"symbols":["ModernFakeTimers"]},"contractCommand":["node","test/contract.mjs"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"npm","executionContext":"node","language":"javascript","libc":"glibc","libcVersion":"2.39","moduleSystem":"cjs","os":"linux","osVersionBucket":"24","packageManager":"npm","packageManagerVersion":"10.9.8","runtime":"node","runtimeVersion":"22.23.2","schemaVersion":1},"license":"MIT-0","packages":["pkg:npm/%40jest/fake-timers@30.4.1"],"schemaVersion":1,"subject":"pkg:npm/%40jest/fake-timers@30.4.1","symbols":["ModernFakeTimers"],"verifierAdapter":"node-typescript@1"}
index.mjs
import { ModernFakeTimers, LegacyFakeTimers } from '@jest/fake-timers';

export { ModernFakeTimers, LegacyFakeTimers };

export function createModernFakeTimers(options = {}) {
  const {
    global = globalThis,
    config = { rootDir: process.cwd() }
  } = options;
  return new ModernFakeTimers({ global, config });
}

export function runWithFakeTime(fn, options = {}) {
  const fakeTimers = createModernFakeTimers(options);
  fakeTimers.useFakeTimers();
  try {
    return fn(fakeTimers);
  } finally {
    fakeTimers.useRealTimers();
  }
}
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package.json
{
  "name": "sample-jest-fake-timers",
  "version": "1.0.0",
  "description": "Clean-room verification sample for @jest/fake-timers",
  "type": "module",
  "main": "index.mjs",
  "scripts": {
    "test": "node test/contract.mjs"
  },
  "dependencies": {
    "@jest/fake-timers": "30.4.1"
  }
}
spec.json
{
  "schemaVersion": 1,
  "goal": "verify pkg:npm/%40jest/fake-timers@30.4.1",
  "kind": "HOW",
  "packages": [
    "pkg:npm/%40jest/fake-timers@30.4.1"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}
test/contract.mjs
import assert from 'node:assert/strict';
import { ModernFakeTimers, LegacyFakeTimers } from '@jest/fake-timers';
import { createModernFakeTimers, runWithFakeTime } from '../index.mjs';

// 1. ModernFakeTimers instantiates with global environment and intercepts timer functions upon useFakeTimers and restores original implementations on useRealTimers
{
  const originalSetTimeout = globalThis.setTimeout;
  const originalDate = globalThis.Date;
  const fake = createModernFakeTimers();
  fake.useFakeTimers();
  assert.notEqual(globalThis.setTimeout, originalSetTimeout);
  assert.notEqual(globalThis.Date, originalDate);
  fake.useRealTimers();
  assert.equal(globalThis.setTimeout, originalSetTimeout);
  assert.equal(globalThis.Date, originalDate);
}

// 2. advanceTimersByTime advances virtual clock by milliseconds and fires scheduled timer callbacks synchronously
{
  const fake = createModernFakeTimers();
  fake.useFakeTimers();
  const calls = [];
  setTimeout(() => { calls.push('a'); }, 250);
  setTimeout(() => { calls.push('b'); }, 500);

  fake.advanceTimersByTime(250);
  assert.deepEqual(calls, ['a']);

  fake.advanceTimersByTime(250);
  assert.deepEqual(calls, ['a', 'b']);
  fake.useRealTimers();
}

// 3. advanceTimersByTimeAsync advances virtual clock asynchronously and resolves pending asynchronous timer callbacks
{
  const fake = createModernFakeTimers();
  fake.useFakeTimers();
  let asyncFired = false;
  setTimeout(() => { asyncFired = true; }, 300);

  assert.equal(asyncFired, false);
  await fake.advanceTimersByTimeAsync(300);
  assert.equal(asyncFired, true);
  fake.useRealTimers();
}

// 4. advanceTimersToNextTimer and advanceTimersToNextTimerAsync progress virtual time directly to the earliest scheduled timer
{
  const fake = createModernFakeTimers();
  fake.useFakeTimers();
  const sequence = [];
  setTimeout(() => { sequence.push(1); }, 100);
  setTimeout(() => { sequence.push(2); }, 300);

  assert.equal(fake.getTimerCount(), 2);
  fake.advanceTimersToNextTimer();
  assert.deepEqual(sequence, [1]);
  assert.equal(fake.getTimerCount(), 1);

  await fake.advanceTimersToNextTimerAsync();
  assert.deepEqual(sequence, [1, 2]);
  assert.equal(fake.getTimerCount(), 0);
  fake.useRealTimers();
}

// 5. runAllTimers and runAllTimersAsync exhaustively execute all queued and recursively scheduled timers
{
  const fake = createModernFakeTimers();
  fake.useFakeTimers();
  const executionOrder = [];
  setTimeout(() => {
    executionOrder.push('parent');
    setTimeout(() => {
      executionOrder.push('child');
    }, 50);
  }, 50);

  fake.runAllTimers();
  assert.deepEqual(executionOrder, ['parent', 'child']);
  assert.equal(fake.getTimerCount(), 0);
  fake.useRealTimers();
}

// 6. runOnlyPendingTimers and runOnlyPendingTimersAsync execute currently queued timers without running newly scheduled nested timers
{
  const fake = createModernFakeTimers();
  fake.useFakeTimers();
  const results = [];
  setTimeout(() => {
    results.push('initial');
    setTimeout(() => {
      results.push('nested');
    }, 50);
  }, 50);

  fake.runOnlyPendingTimers();
  assert.deepEqual(results, ['initial']);
  assert.equal(fake.getTimerCount(), 1);

  fake.clearAllTimers();
  assert.equal(fake.getTimerCount(), 0);
  fake.useRealTimers();
}

// 7. clearAllTimers and getTimerCount track and cancel active scheduled timers
{
  const fake = createModernFakeTimers();
  fake.useFakeTimers();
  setTimeout(() => {}, 100);
  setTimeout(() => {}, 200);
  setInterval(() => {}, 300);

  assert.equal(fake.getTimerCount(), 3);
  fake.clearAllTimers();
  assert.equal(fake.getTimerCount(), 0);
  fake.useRealTimers();
}

// 8. setSystemTime, now, and reset manage and simulate current timestamp
{
  const fake = createModernFakeTimers();
  fake.useFakeTimers();
  const epochTime = new Date('2026-08-23T12:00:00.000Z').getTime();
  fake.setSystemTime(epochTime);

  assert.equal(fake.now(), epochTime);
  assert.equal(Date.now(), epochTime);

  fake.reset();
  assert.equal(fake.now(), epochTime);
  fake.useRealTimers();
}

// 9. setTimerTickMode configures timer advance behavior
{
  const fake = createModernFakeTimers();
  fake.useFakeTimers();
  fake.setTimerTickMode({ mode: 'manual' });
  let ticked = false;
  setTimeout(() => { ticked = true; }, 100);
  fake.advanceTimersByTime(100);
  assert.equal(ticked, true);
  fake.useRealTimers();
}

// 10. runWithFakeTime helper safely executes a scoped callback and restores native timers
{
  const originalSetTimeout = globalThis.setTimeout;
  let executed = false;
  runWithFakeTime(fakeTimers => {
    assert.notEqual(globalThis.setTimeout, originalSetTimeout);
    setTimeout(() => { executed = true; }, 100);
    fakeTimers.runAllTimers();
    assert.equal(executed, true);
  });
  assert.equal(globalThis.setTimeout, originalSetTimeout);
}

console.log('All @jest/fake-timers contract assertions passed.');

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