How to reset Jest mock functions calls count before every test

Question

I'm new to Jest, I'm trying to use it for testing if a function was called or not. I noticed the mock.calls.length is not resetting for every test but accumulating. How can I make it 0 before every test? I don't want my next tests depends on the results of the previous.

I know there is beforeEach in Jest - should I use it? What is the best way to reset mock.calls.length? Thank you.

A code example:

Sum.js:

import local from 'api/local';

export default {
  addNumbers(a, b) {
    if (a + b <= 10) {
      local.getData();
    }
    return a + b;
  },
};

Sum.test.js

import sum from 'api/sum';
import local from 'api/local';
jest.mock('api/local');

// For current implementation, there is a difference 
// if I put test 1 before test 2. I want it to be no difference

// test 1
test('should not to call local if sum is more than 10', () => {
  expect(sum.addNumbers(5, 10)).toBe(15);
  expect(local.getData.mock.calls.length).toBe(0);
});

// test 2
test('should call local if sum <= 10', () => {
  expect(sum.addNumbers(1, 4)).toBe(5);
  expect(local.getData.mock.calls.length).toBe(1);
});

Answer 1

One way I found to handle it: to clear mock function after each test:

To add to Sum.test.js:

afterEach(() => {
  local.getData.mockClear();
});

If you'd like to clear all mock functions after each test, use clearAllMocks

afterEach(() => {
  jest.clearAllMocks();
});

Answer 2

As @AlexEfremov pointed in the comments. You may want to use clearAllMocks after each test:

afterEach(() => {
    jest.clearAllMocks();
});

Take in mind this will clear the call count of every mock function you have, but that is probably the right way.

Answer 3

You can configure Jest to reset or clear mocks after each test by putting one of these parameters this into your jest.config.js :

module.exports = {
  resetMocks: true,
};

or

module.exports = {
  clearMocks: true,
};

Here is the documentation:

https://jestjs.io/docs/en/configuration#resetmocks-boolean

resetMocks [boolean]

Default: false

Automatically reset mock state before every test. Equivalent to calling jest.resetAllMocks() before each test. This will lead to any mocks having their fake implementations removed but does not restore their initial implementation.

https://jestjs.io/docs/configuration#clearmocks-boolean

clearMocks [boolean]

Default: false

Automatically clear mock calls, instances and results before every test. Equivalent to calling jest.clearAllMocks() before each test. This does not remove any mock implementation that may have been provided.

Answer 4

jest.clearAllMocks(); didn't clear all the mocks actually for me.

afterEach(() => {
    jest.restoreAllMocks();
}); 

helped me finally clear the spy on jest

Answer 5

clear the individual mocked function after each test, (this may be usefull for someone hitting this url)

import { methodName } from '../Path-to-file-with-methodName';

methodName.mockReturnValue(null );

    describe('my component', ()=> {
      afterEach(() => {
        methodName.mockClear();
      });
      
      it('should call my method on mount', () => {
        const wrapper = mount(<AComponent  {...props} />);
        expect(methodName).toHaveBeenCalledTimes(1);
      })
      it('should call my method on mount again', () => {
        const wrapper = mount(<AComponent  {...props} />);
        expect(methodName).toHaveBeenCalledTimes(1);
      })
    });

 

Answer 6

You can add the --resetMocks option to the command: npx jest --resetMocks

Automatically reset mock state between every test. Equivalent to calling jest.resetAllMocks()