Mocking moment() and moment().format using jest

Question

I\'m unable to mock moment() or moment().format functions. I have states where, currentDateMoment and currentDateFormatted ar

Answer 1

Here is the solution:

index.ts:

import moment from 'moment';

export function main() {
  return {
    currentDateMoment: moment().format(),
    currentDateFormatted: moment()
      .format('MM-DD-YYYY')
      .valueOf()
  };
}

index.spec.ts:

import { main } from './';
import moment from 'moment';

jest.mock('moment', () => {
  const mMoment = {
    format: jest.fn().mockReturnThis(),
    valueOf: jest.fn()
  };
  return jest.fn(() => mMoment);
});

describe('main', () => {
  test('should mock moment() and moment().format() correctly ', () => {
    (moment().format as jest.MockedFunction)
      .mockReturnValueOnce('2018–01–30T12:34:56+00:00')
      .mockReturnValueOnce('01–30-2018');
    expect(jest.isMockFunction(moment)).toBeTruthy();
    expect(jest.isMockFunction(moment().format)).toBeTruthy();
    const actualValue = main();
    expect(actualValue).toEqual({ currentDateMoment: '2018–01–30T12:34:56+00:00', currentDateFormatted: '01–30-2018' });
  });
});

Unit test result with 100% coverage:

 PASS  src/stackoverflow/55838798/index.spec.ts
  main
    ✓ should mock moment() and moment().format() correctly  (7ms)

----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |      100 |      100 |      100 |      100 |                   |
 index.ts |      100 |      100 |      100 |      100 |                   |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        3.795s, estimated 8s

Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/55838798