Mock Date when run unit test cases with jest. Make tests of Date easier.

• jest-random-mock Mock Math.random in jest, with deterministic random generator.
• jest-canvas-mock Mock canvas when run unit test cases with jest.

This should only be installed as a development dependency (devDependencies) as it is only designed for testing.

npm i --save-dev jest-date-mock

In your package.json under the jest, create a setupFiles array and add jest-date-mock to the array.

{ "jest": { "setupFiles": ["jest-date-mock"] } }

If you already have a setupFiles attribute you can also append jest-date-mock to the array.

{ "jest": { "setupFiles": ["./__setups__/other.js", "jest-date-mock"] } }

More about in configuration section.

Alternatively you can create a new setup file which then requires this module or add the require statement to an existing setup file.

__setups__/date.js

import 'jest-date-mock'; // or require('jest-date-mock');

Add that file to your setupFiles array:

"jest": { "setupFiles": [ "./__setups__/date.js" ] }

Use the only 3 api for test cases.

• advanceBy(ms): advance date timestamp by ms.
• advanceTo([timestamp]): reset date to timestamp, default to 0.
• clear(): shut down the mock system.

import { advanceBy, advanceTo, clear } from 'jest-date-mock'; test('usage', () => { advanceTo(new Date(2018, 5, 27, 0, 0, 0)); // reset to date time. const now = Date.now(); advanceBy(3000); // advance time 3 seconds expect(+new Date() - now).toBe(3000); advanceBy(-1000); // advance time -1 second expect(+new Date() - now).toBe(2000); clear(); Date.now(); // will got current timestamp });

More sample code here.

Also, add an API Date.current() to get the actual current timestamp.

import { advanceBy, advanceTo, clear } from 'jest-date-mock'; advanceTo(0); // reset to timestamp = 0 Date.now(); // will got 0 Date.current(); // will got the actual timestamp.

MIT@hustcc.