CODEWITHSUNDEEP
jestjs
James Ives
James Ives

Reputation: 3365

Check if a function has fired in Jest

I have a class which starts and fires off a setup function in the constructor like so:

import { myFunction } from './util';

export class MyClass {
  constructor() {
    myFuction()
  }
}

And then inside that function I have this:

export function myFunction() {
  window.fruit = 'apple';
}

I want to test in Jest that the myFunction() function gets fired, and that window.fruit has the property of Apple. 

import MyClass from '../index';
import { myFunction } from '../util';

describe('myclass', () => {
  const mocks = {
    myFunction: jest.fn()
  }

  const meinclass = new MyClass();

  describe('#constructor', () => {
    it('should initialize the class', () => {
      expect(meinclass).not.toBeUndefined()
    })

    it('should call myfunction', () => {
      const init = jest.spyOn(myFunction);
      const fruit = window.fruit

      expect(init).toHaveBeenCalled()
      expect(fruit).toBe('apple')
    })
  })

})

I am unsure of the correct way of testing this? I've tried using the .mock method of Jest also but I seem to be struggling to get it to work. Whenever I even log window I don't see the property fruit on it. I feel like there's a larger part of this puzzle I'm missing. Apologies for the simple question.

Upvotes: 0

Views: 2777

Answers (1)

Andreas Köberle
Andreas Köberle

Reputation: 110922

I don't think it make sense to test both, that the function was called and that window.fruit was set correctly. So instead of using window use global. Doing it this way you don't need to mock anything.

it('should call myfunction', () => {
  const fruit = global.fruit
  expect(fruit).toBe('apple')
})

The other way would be only to test that the function was called:

import MyClass from '../index';
import { myFunction } from '../util';

jest.mock('../util', ()=>({myFunction: jest.fn()}))

it('should call myfunction', () => {
  expect(myFunction).toHaveBeenCalled()
})

Upvotes: 1

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