smartlyio / fake-time

jest fake timers AND(!!!11) Date.now at the same time. Magic.

fake-time

Fake time AND timers in jest. This here thing aims to solve three(!) problems

• Jest advanceTimersTo does not change the time Date.now gives out.
• Jest timer mocks either run the timers once or runs the all timers to exhaustion both of which result in funny if your timers set up new timers
• Jest timer mocks do not run promises from the promise jobs queue which causes setting new timers from promisy code really annoying.

A working example

// yarn jest examples/working.ts
import * as fakeTime from '../index';

describe('fake-time', () => {
  beforeEach(fakeTime.fake);
  afterAll(fakeTime.restore);

  it('advances time', async () => {
    const start = Date.now();
    await fakeTime.advance(1000);
    expect(Date.now() - start).toBeGreaterThan(1000);
  });

  it('runs promises and new timers from timers', async () => {
    const interval = 10;
    let hits = 0;
    async function set() {
      hits++;
      await Promise.resolve();
      setTimeout(set, interval);
    }
    await set();
    await fakeTime.advance(interval * 10);
    expect(hits).toBeGreaterThan(10);
  });

  describe('wait', () => {
    const dayInMs = 24 * 60 * 50 * 1000;

    it('advances time while waiting', async () => {
      const start = Date.now();
      await fakeTime.wait(async () => expect(Date.now() - start).toBeGreaterThan(dayInMs), {
        untilMs: dayInMs * 2 * 10,
      });
    });
  });
});

fake-time's Issues

Action Required: Fix Renovate Configuration

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Error type: Cannot find preset's package (github>smartlyio/renovate-config:security-base)

Dependency Dashboard

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Warning

These dependencies are deprecated:

Datasource	Name	Replacement PR?
npm	tslint

Awaiting Schedule

These updates are awaiting their schedule. Click on a checkbox to get an update now.

• Update dependency @types/node to v20.14.15

Open

These updates have all been created already. Click a checkbox below to force a retry/rebase of any.

• Update actions/checkout action to v4
• Update actions/setup-node action to v4

Detected dependencies

github-actions

.github/workflows/nodejs.yml

• actions/checkout v3
• actions/setup-node v3

npm

package.json

• @types/jest 29.5.12
• @types/node 20.14.14
• jest 29.7.0
• jsverify 0.8.4
• prettier 3.3.3
• ts-jest 29.2.4
• ts-node 10.9.2
• tslint 6.1.3
• tslint-config-prettier 1.18.0
• tslint-plugin-prettier 2.3.0
• typescript 5.5.4
• jest ^29.0.0

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