How to write unit test case for my cron job Scheduler

Question

I've updated my cron job scheduler function. Now i need to update the unit test case for this function. For scheduleJob passing date and function as params. In my test case, I need to check whether the function toHaveBeenCalled .

/**
 * @file Scheduler Service.
 */

// Import External Modules
import { CronCommand, CronJob } from 'cron';

// ************* Scheduler Configuration ***************
const TIMEZONE = 'Asia/Kolkata';
// *****************************************************

export class Scheduler {
  static scheduleJob = (scheduleDate: Date, scheduleFunction: CronCommand) => {
    const date = new Date(scheduleDate);
    const scheduleJob = new CronJob(
      `0 0 0 ${date.getDate()} ${date.getMonth()} 0-6`,
      scheduleFunction,
      undefined,
      true,
      TIMEZONE,
    );
    scheduleJob.start();
  };
}

Answer 1

You can use jest.mock(moduleName, factory, options) mock the CronJob constructor and its instance for cron module.

Eg

index.ts :

import { CronCommand, CronJob } from 'cron';

// ************* Scheduler Configuration ***************
const TIMEZONE = 'Asia/Kolkata';
// *****************************************************

export class Scheduler {
  static scheduleJob = (scheduleDate: Date, scheduleFunction: CronCommand) => {
    const date = new Date(scheduleDate);
    const scheduleJob = new CronJob(
      `0 0 0 ${date.getDate()} ${date.getMonth()} 0-6`,
      scheduleFunction,
      undefined,
      true,
      TIMEZONE,
    );
    scheduleJob.start();
  };
}

index.test.ts :

import { Scheduler } from '.';
import { CronJob } from 'cron';

jest.mock('cron', () => {
  const mScheduleJob = { start: jest.fn() };
  const mCronJob = jest.fn(() => mScheduleJob);
  return { CronJob: mCronJob };
});

describe('62078071', () => {
  it('should pass', () => {
    const mScheduleJob = new CronJob();
    const mDate = new Date(1995, 11, 17);
    const mScheduleFunction = jest.fn();
    Scheduler.scheduleJob(mDate, mScheduleFunction);
    expect(CronJob).toBeCalledWith(`0 0 0 17 11 0-6`, mScheduleFunction, undefined, true, 'Asia/Kolkata');
    expect(mScheduleJob.start).toBeCalledTimes(1);
  });
});

The outcome for the test:

 PASS  stackoverflow/62078071/index.test.ts (14.62s)
  62078071
    ✓ should pass (8ms)

----------|---------|----------|---------|---------|-------------------
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:        16.582s