Mock specific config value in jest

Question

I have the following default/config.js file

/* eslint-disable @typescript-eslint/no-var-requires */
require('dotenv').config({
  path: require('find-config')('.env'),
});

module.exports = {
  cronInterval: process.env.CRON_INTERVAL,
  queueName: process.env.QUEUE_NAME || '',
  isVisible: process.env.IS_VISIBLE
};

In my index.ts, I have

import config from 'config';
import * as cron from 'node-cron';

const isVisible = config.get<boolean>('isVisible');
const queueName = config.get<string>('queueName');
const cronInterval = config.get<string>('cronInterval');

function startProcess(queueName) {
    cron.schedule(cronInterval, () => {});
}

// process starts here
if (isVisible) {
  startProcess(queueName);
} else {
  logger.info('Wont start')
}

In my unit tests I want to test for both cases of isVisible, while keeping the other config values as they are.

I tried

describe.only('isVisible', () => {
    beforeEach(() => {
        jest.mock('./../config/default.js', () => ({ 
            isVisible: false
        }));
    })
    it('should not run anything if not visible', () => {
        require('./../src/index');
        const scheduleSpy = jest.spyOn(cron, 'schedule');
        expect(scheduleSpy).not.toHaveBeenCalled();
    })
})

This didnt work for me, and it doesnt override the value of isVisible.

I know I could also mock the config.get function like config.get.mockReturnValue(false), but that would then override the values of cronInterval and queueName

Cherenkov

Where does the config.get() method come from? How did you import config module in your index.ts file? – Mawson

@slideshowp2 it's the config package npmjs.com/package/config – Cherenkov

@AngularDebutant, please change const to let for isVisible and import that file and try to change its value. – Futures

You know there's a typo on your code, right? "isVibible: false" – Capacitate

Answer 1

Here's one way I recently solved a similar need (conditionally needing the original module functionality) ...

let isVisible = false;

jest.mock('config', () => {
  // Require the original module!
  const originalConfig = jest.requireActual('config');

  return {
    __esModule: true, // for esModules
    get: jest.fn((key: string) => {
      // override result conditionally on input arguments
      if (key === 'isVisible') return isVisible;
      // otherwise return using original behavior
      return originalConfig.get(key);
    })
  };
});

Then in your tests:

it('isVisible=true', () => {
  isVisible = true;
  // test logic here
});

it('isVisible=false', () => {
  isVisible = false;
  // test logic here
});

Voyeurism

Thanks, but for some reason, only the first test runs. I dont know if it has something to do with the require('./../src/index'); ? but the code in the file is called only once for both tests.. – Cherenkov

Mocking only knows about the path you give it... Sorequire('./../src/index') is different from require('config'). Also, as a general rule, it's easier to mock functions - rather than exported objects/arrays. – Voyeurism

I ended up doing things a bit differently, but I accepted your answer as it solves the original question. Thanks. – Cherenkov