jest-plugin-clock

jest-plugin-clock

Jest plugin to mock dates, times, and datetimes.

Getting Started

Install jest-plugin-clock using yarn:

yarn add --dev jest-plugin-clock

Motivation

When testing dates, you often want to have deterministic outcomes even when using new Date() and Date.now(). This allows you to set the clock time such that your test can compute the deterministic outcome each time.

Usage

If you want, you can import clock from jest-plugin-clock at the top of every test:

import clock from 'jest-plugin-clock';

If you want to install clock as a global, you can modify the jest section of your package.json to include:

"jest": {
  "setupFiles": [
    "jest-plugin-clock/setup"
  ]
}

Example

Here's an example test that tests clock itself:

describe('clock', () => {
  context('with string date', () => {
    clock.set('2017-08-16T15:20:40.450');

    it('returns the correct year', () => {
      expect(new Date().getFullYear()).toEqual(2017);
    });

    it('returns the correct month', () => {
      // getMonth is 0-indexed.
      expect(new Date().getMonth()).toEqual(7);
    });

    it('returns the correct day (date)', () => {
      expect(new Date().getDate()).toEqual(16);
    });

    it('returns the correct hour', () => {
      expect(new Date().getHours()).toEqual(15);
    });

    it('returns the correct minute', () => {
      expect(new Date().getMinutes()).toEqual(20);
    });

    it('returns the correct seconds', () => {
      expect(new Date().getSeconds()).toEqual(40);
    });

    it('returns the correct milliseconds', () => {
      expect(new Date().getMilliseconds()).toEqual(450);
    });
  });

  context('with date object', () => {
    clock.set(new Date('2017-08-16T15:20:40.450'));

    it('returns the correct year', () => {
      expect(new Date().getFullYear()).toEqual(2017);
    });

    it('returns the correct month', () => {
      // getMonth is 0-indexed.
      expect(new Date().getMonth()).toEqual(7);
    });

    it('returns the correct day (date)', () => {
      expect(new Date().getDate()).toEqual(16);
    });

    it('returns the correct hour', () => {
      expect(new Date().getHours()).toEqual(15);
    });

    it('returns the correct minute', () => {
      expect(new Date().getMinutes()).toEqual(20);
    });

    it('returns the correct seconds', () => {
      expect(new Date().getSeconds()).toEqual(40);
    });

    it('returns the correct milliseconds', () => {
      expect(new Date().getMilliseconds()).toEqual(450);
    });
  });
});