CODEWITHSUNDEEP
javascriptreactjsjestjs
abc
abc

Reputation: 41

How to properly mock a node module for jest unit testing

I'm new to jest and just want to implement a unit test for a simple function that uses a third party node module.

function to test (say it lives in utilFolder.js):

import moduleName from 'third_party_module'
const util = {
   simple_function() {
      const name = moduleName.func1();
   }
}

export default util;

test file:

import util from "utilFolder";
import moduleName  from 'third_party_module';
jest.mock("third_party_module", () => ({
   func1: jest.fn()
}));

describe("was mocked functions called", () {
  test("was mocked functions called??", () => {
      util.simple_function();
      expect(moduleName.func1).toHaveBeenCalled();
  });
});

Error:

Expected mock function to have been called, but it was not called.

Any help please?

Upvotes: 4

Views: 1219

Answers (1)

Lin Du
Lin Du

Reputation: 102257

Use jest.mock mock the module. Here is the working example:

util.js:

import moduleName from './third_party_module';

const util = {
  simple_function() {
    const name = moduleName.func1();
  }
};

export default util;

third_party_module.js:

export default {
  func1() {}
};

util.spec.js:

import util from './util';
import moduleName from './third_party_module';

jest.mock('./third_party_module', () => ({
  func1: jest.fn()
}));

describe('was mocked functions called', () => {
  test('was mocked functions called??', () => {
    util.simple_function();
    expect(moduleName.func1).toHaveBeenCalled();
  });
});

Unit test result:

 PASS  src/stackoverflow/54729837/util.spec.js (8.414s)
  was mocked functions called
    ✓ was mocked functions called?? (4ms)

Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        9.742s

Source code: https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/54729837

Upvotes: 1

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