How to mock uuid with Jest

Question

so on my search for an answer to my problem I found this post: Jest: How to globally mock node-uuid (or any other imported module)

I already tried the answer but I can't seem to use it properly, as it´s giving me an undefined error. I'm new to the testing scene so please excuse any major errors:

This was my first approach

const mockF = jest.mock('uuid'); 

mockF.mockReturnValue('12345789'); 

But it wouldn't recognize the functions.

"mockF.mockReturnValue is not a function" among others I tried.

Then I tried to manually mock as the post suggested but can' seem to make it work, can you help me? Thanks

Here's the entire test if it helps:

    const faker = require('faker');
    const storageUtils = require('../../storage/utils');
    const utils = require('../utils/generateFile');
    const { generateFileName } = storageUtils;
    const { file } = utils;

    test('should return a valid file name when provided the correct information', () => {
        // ARRANGE
        // create a scope
        const scope = {
            type: 'RECRUITER',
            _id: '987654321',
        };
        // establish what the expected name to be returned is
        const expectedName = 'r_987654321_123456789.png';

        jest.mock('uuid/v4', () => () => '123456789');

        // ACTION
        const received = generateFileName(file, scope);

        // ASSERT
        // expect the returned value to equal our expected one
        expect(received).toBe(expectedName);
    });

Answer 1

Mock it by using mockImplementation.

import uuid from 'uuid/v4';
jest.mock('uuid/v4');

describe('mock uuid', () => {
  it('should return testid }', () => {
    uuid.mockImplementation(() => 'testid');
    ...
  });  
});

Make sure you import uuid correctly (with correct version reference e.g. v4, v3...)

Answer 2

Assuming the following test file, you can use the jest.spyOn call to mock out uuid.

Test.spec.js

import uuid from 'uuid';
import testTarget from './testTarget';

describe('mock uuid', () => {
  it('should return testid }', () => {
    // Arrange
    const anonymousId = 'testid';
    const v1Spy = jest.spyOn(uuid, 'v1').mockReturnValue(anonymousId);

    // Act
    const result = testTarget();

    // Assert
    expect(result).toEqual(anonymousId);
    expect(v1Spy).toHaveBeenCalledTimes(1);
  });  
});

testTarget.js

import uuid from 'uuid';
export default function() {
   return uuid.v1();
}

Answer 3

for my case I used the answer of this Github issue

jest.mock('uuid/v4', (): () => number => {
 let value = 0;
 return () => value++;
});

Answer 4

import uuid from 'uuid'

describe('some test', () => {
  it('some test 1', () => {
     const uuidMock = jest.spyOn(uuid, 'v4').mockReturnValue('123434-test-id-dummy');

     // expect(uuidMock).toHaveBeenCalledTimes(<number of times called>);

  })
})

Answer 5

It's really well explained in the documentation, but in general you can:

const mockF = jest.fn().mockReturnValue('12345789');

or

import uuid from 'uuid';
jest.mock('uuid', () => 
    jest.fn().mockReturnValue('12345789');
);