Is it right solution to use separate package for setting timezone? I don't understand from where moment gets timezone, tried to mock Date.prototype.getTimezoneOffset , but looks like moment don't uses it. Also founded that for negative offset tests not fails, only if my offset is more than 0 tests fails.

I had to use require instead of requireActual otherwise I would get moment.tz === undefined

const moment = require('moment-timezone');
jest.doMock('moment', () => {
  moment.tz.setDefault('Asia/Yekaterinburg');
  return moment;
});

Add the following before describe in your test
const moment = require.requireActual('moment-timezone').tz.setDefault('America/Los_Angeles');

If you are using guess to check use current timezone, you also need to mock it:

jest.mock('moment-timezone', () => {
    const momentMock = require.requireActual('moment-timezone');
    momentMock.tz.setDefault('America/Los_Angeles'); // Whatever timezone you want
    momentMock.tz.guess = () => 'America/Los_Angeles'; // Whatever timezone you want
    return momentMock;
});

I noticed that requireActual of module A (in our case moment-timezone) inside the mock of module B (moment) returns an empty object.

jest.mock('moment', () => {
  const moment = require.requireActual('moment-timezone')
  console.log(require.requireActual('moment-timezone')) // logs {}
  console.log(require.requireActual('moment')) // logs the actual moment library 
})

Anybody facing the same problem ?

@adica - that code worked for me! The only issue I ran into thereafter (removed my manual import of moment-timezone in the spec file) was not being able to call moment() for new dates in my spec file; ended up using a different approach there.

Had the same error as @a-reda, the following code worked for me:

// setup.js
const moment = require('moment-timezone')
moment.tz.setDefault('Antarctica/Vostok') // Whatever timezone you want
jest.setMock('moment', moment)

This gist was of great help to me. I found another way of mocking the timezone with a fixed value.

jest.mock('moment', () => () => (jest.requireActual('moment-timezone')).tz('2021-01-01T00:00:00.000Z', 'GMT'));

Hi i tried const moment = require('moment-timezone')
moment.tz.setDefault('Antarctica/Vostok') // Whatever timezone you want
jest.setMock('moment', moment)
it is giving me original user's time zone not the mocked one
any one please help me

export class DateTzPipe implements PipeTransform {
transform(x: any) {
const y = moment.tz(x, 'America/Panama').format();
const errorDate = new Date(y);
const timeZoneString = moment.tz.guess() === 'Pacific/Port_Moresby' ? 'CHST' : moment.tz(moment.tz.guess()).format('z');
return (moment.tz(errorDate,moment.tz.guess()).format('MM/DD/YYYY - hh:mm:ss A') + " " + timeZoneString);

}

test:
const moment = require('moment-timezone')
moment.tz.setDefault('America/New_york') // Whatever timezone you want
jest.setMock('moment', moment)
describe('transform', () => {
let datePipe:DateTzPipe;

beforeEach(() => {
  
  datePipe=new DateTzPipe();
});



it('Should transform measures without a strat expression', () => {
      expect(datePipe.transform('2021-09-07T19:23:44.309871')).toBe('09/07/2021 - 08:23:44 PM EDT');
});

If you're still struggling with timezones, try this https://www.npmjs.com/package/timezone-mock it saved my day.

@pimlie thank you! Your solution works

None of these worked for me. I realized this is simply the wrong approach (depending on what you need).

I ended up doing this instead:

test('test thing', () => {
  jest.useFakeTimers();
  jest.setSystemTime(new Date('2023-01-01'));
  expect(fn).toEqual(thing);
  jest.setSystemTime(new Date());
});

IMHO, it is best to avoid monkey-patching moment.