如何在开玩笑测试中模拟 moment()

Question

I need run some testing using jest and moment. Some of the imported functions work with moment current date (moment() ). But I can't seem to find a way of always run the same date for testing or mock moment constructor, like pin moment date at moment('2020-07-05'), even if current day is 2020-07-10, so the test should always run under day 5.

My./UtilsModule file:

import moment from 'moment'
export const getIntervalDates = groupOfDates => {
   const CURRENT_DATE = moment().format('YYYY-MM-DD');
   return getDates(CURRENT_DATE, groupOfDates ) //another function that does some extra processing;
};

export const nextDates = (date, group) => {
  let newDate= getIntervalDates(group);
}

My test.js file, and what i tried for:

import { nextDates ,getIntervalDates } from '../UtilsModule';
it('testing function', () => {
      const PAYLOAD = {...};
      const DATE= '2020-07-20';

      const SpyGetIntervalDates = jest.spyOn(UtilsModule, 'getIntervalDates');
      SpyGetIntervalDates.mockImplementation(() => Promise.resolve({ minAge: '2020-08-04' }));

      const nextDate = UtilsModule.nextDates(DATE, PAYLOAD);
      expect(nextDate).toEqual({ minDate: '2020-11-04' });
    });

I also tried, but i couldn't make it to work:

jest.mock('moment', () => {
  return () => jest.requireActual('moment')('2020-07-04');
});

and
global.moment = jest.fn(moment('2021-07-04'));

Answer 1

You were trying to test nextDates function with mocked getIntervalDates function. You need to do a little refactoring, you should keep the same reference for getIntervalDates function called inside nextDates . Then, you can use jest.spyOn to replace getIntervalDates with a mocked one.

Eg

utilsModule.js :

import moment from 'moment';

function getDates() {}

const getIntervalDates = (groupOfDates) => {
  const CURRENT_DATE = moment().format('YYYY-MM-DD');
  return getDates(CURRENT_DATE, groupOfDates);
};

const nextDates = (date, group) => {
  return exports.getIntervalDates(group);
};

exports.getIntervalDates = getIntervalDates;
exports.nextDates = nextDates;

utilsModule.test.js :

const UtilsModule = require('./utilsModule');

describe('62736904', () => {
  it('testing function', async () => {
    const PAYLOAD = {};
    const DATE = '2020-07-20';

    const SpyGetIntervalDates = jest.spyOn(UtilsModule, 'getIntervalDates');
    SpyGetIntervalDates.mockImplementation(() => Promise.resolve({ minAge: '2020-08-04' }));

    const nextDate = await UtilsModule.nextDates(DATE, PAYLOAD);
    expect(nextDate).toEqual({ minAge: '2020-08-04' });
  });
});

unit test result:

 PASS  stackoverflow/62736904/utilsModule.test.js (11.51s)
  62736904
    ✓ testing function (3ms)

----------------|---------|----------|---------|---------|-------------------
File            | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------------|---------|----------|---------|---------|-------------------
All files       |      75 |      100 |   33.33 |      75 |                   
 utilsModule.js |      75 |      100 |   33.33 |      75 | 6-7               
----------------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        12.892s