Jest jest.mock function with different return value

Question

testing react and typescript with jest and enzyme, how would I mock this expectsVideo function such that I can define if it returns true of false based on my test case scenerio

jest.mock('utils/media-utils', () => ({
  expectsVideo: () => true,
  myOtherFunctions: jest.fn()
}));

the utils/media-utils if a file that is being imported in the react component that I am testing. If I try to reference object from outside it gives me error stating cannot use out of scope variables. Tried various implementation i came across different blogs but no help.

skyboyer · Accepted Answer · 2018-10-08 22:35:14Z

5

mockImplementation should help while mocking whole module:

import * as mediaUtils from 'utils/media-utils';

mock('utils/media-utils'); // automocking whole module

it('....1...', () => {
    mediaUtils.expectsVideo.mockImplementation(() => true);
});

it('....2...', () => {
    mediaUtils.expectsVideo.mockImplementation(() => false);
});

BTW as for referencing variables from outer that returns error(from section for jest.doMock documentation):

When using babel-jest, calls to mock will automatically be hoisted to the top of the code block. Use this method if you want to explicitly avoid this behavior.

So that's why all const and let are not even defined at point when module is mocked.

answered Oct 8, 2018 at 22:35

skyboyer

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