jest-mock.test.js

// [email protected] while working on [email protected]
describe('setState mock test', () => {
  let mockCallback;
  let setState;

  const receiver = {
    state: {
      disabled: false,
    },
    setState(state, callback) {
      this.state = { ...this.state, ...state }
      callback && callback()
    },
  }
  const receiver_working = {
    state: {
      disabled: false,
    },
    setState(state, callback) {
      this.state = { ...this.state, ...state }
      callback && callback()
    },
  }
  // spyOn before test cases which is not working but why?
  // jest.spyOn(receiver, 'setState', { callThrough: true })
  jest.spyOn(receiver, 'setState').mockImplementation((state, callback) => {
    receiver.state = { ...receiver.state, ...state }
    callback && callback()
  })
  setState = receiver.setState
  console.log('setState=', setState);

  beforeEach(() => {
    // spyOn in beforeEach which is working
    jest.spyOn(receiver_working, 'setState').mockImplementation((state, callback) => { 
        receiver_working.state = { ...receiver_working.state, ...state }
        callback && callback()
        // this will cause looping by calling the mock implementation again
        //return receiver_working.setState.apply(this, [state, callback]);
    })
    mockCallback = jest.fn();
  });

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

  test('callback should be called', () => {
    receiver_working.setState({ disabled: true }, () => { mockCallback(); console.log('setState called'); });
    expect(mockCallback).toHaveBeenCalled();
  })

  test('callback is not called', () => {
    receiver.setState({ disabled: true }, () => { mockCallback(); console.log('setState called'); });
    expect(mockCallback).not.toHaveBeenCalled();
  });
});