how to change jest mock function return value in each test?

问题

I have a mock module like this in my component test file

  jest.mock('../../../magic/index', () => ({
    navigationEnabled: () => true,
    guidanceEnabled: () => true
  }));

these functions will be called in render function of my component to hide and show some specific feature.

I want to take a snapshot on different combinations of the return value of those mock functions.

for suppose I have a test case like this

 it('RowListItem should not render navigation and guidance options', () => {
    const wrapper = shallow(
      <RowListItem type="regularList" {...props} />
    );
    expect(enzymeToJson(wrapper)).toMatchSnapshot();
  });

to run this test case I want to change the mock module functions return values to false like this dynamically

jest.mock('../../../magic/index', () => ({
    navigationEnabled: () => false,
    guidanceEnabled: () => false
  }));

because i am importing RowListItem component already once so my mock module wont re import again. so it wont change. how can i solve this ?

回答1:

You can mock the module so it returns spies and import it into your test:

import {navigationEnabled, guidanceEnabled} from '../../../magic/index'

jest.mock('../../../magic/index', () => ({
    navigationEnabled: jest.fn(),
    guidanceEnabled: jest.fn()
}));

Then later on you can change the actual implementation using mockImplementation

navigationEnabled.mockImplementation(()=> true)
//or
navigationEnabled.mockReturnValueOnce(true);

and in the next test

navigationEnabled.mockImplementation(()=> false)
//or
navigationEnabled.mockReturnValueOnce(false);

回答2:

what you want to do is

import { navigationEnabled, guidanceEnabled } from '../../../magic/index';   

jest.mock('../../../magic/index', () => ({
  navigationEnabled: jest.fn(),
  guidanceEnabled: jest.fn()
}));

describe('test suite', () => {
  it('every test', () => {
    navigationEnabled.mockReturnValueOnce(value);
    guidanceEnabled.mockReturnValueOnce(value);
  });
});

you can look more about these functions here =>https://facebook.github.io/jest/docs/mock-functions.html#mock-return-values

回答3:

I had a hard time getting the accepted answers to work - my equivalents of navigationEnabled and guidanceEnabled were undefined when I tried to call mockReturnValueOnce on them.

Here's what I had to do:

In ../../../magic/__mocks__/index.js:

export const navigationEnabled = jest.fn();
export const guidanceEnabled = jest.fn();

in my index.test.js file:

jest.mock('../../../magic/index');
import { navigationEnabled, guidanceEnabled } from '../../../magic/index';
import { functionThatReturnsValueOfNavigationEnabled } from 'moduleToTest';

it('is able to mock', () => {
  navigationEnabled.mockReturnValueOnce(true);
  guidanceEnabled.mockReturnValueOnce(true);
  expect(functionThatReturnsValueOfNavigationEnabled()).toBe(true);
});

来源：https://stackoverflow.com/questions/45758366/how-to-change-jest-mock-function-return-value-in-each-test

标签

reactjs

react-native

jestjs

enzyme