Jest spy on functionality

Solution 1:

Actually you can use jest.spyOn jest.spyOn

If method is called when component created use:

import { mount } from 'enzyme'; 

describe('My component', () => {
  it('should call getData', () => {
    const spy = jest.spyOn(Component.prototype, 'getData');
    mount(<Component />);
    expect(spy).toHaveBeenCalledTimes(1)
  });
})

or if you have it in your DOM and method use bind you can use:

import { shallow } from 'enzyme'; 

describe('My component', () => {
  it('should call getData', () => {
    const wrapper = shallow(<Component />);
    const instance = wrapper.instance()
    const spy = jest.spyOn(instance, 'getData');
    wrapper.find('button').simulate('click')
    expect(spy).toHaveBeenCalledTimes(1)
  });
})

Solution 2:

There is the spyOn method, that was introduced with v19 some days ago, that does exactly what you are looking for

Solution 3:

You could go for the new spyOn method or the following should also work fine.

it('should call getData', () => {
    Component.prototype.getData = jest.fn(Component.prototype.getData);
    expect(Component.prototype.getData).toBeCalled();
});

Solution 4:

I'm using Jest with React 16.8 - This worked for me:

  it("lifecycle method should have been called", () => {
    jest.spyOn(RedirectingOverlay.prototype, 'componentWillUnmount');
    jest.spyOn(RedirectingOverlay.prototype, 'componentDidMount');
    const wrapper = mount(<RedirectingOverlay message="Hi There!"/>);
    expect(RedirectingOverlay.prototype.componentDidMount).toHaveBeenCalledTimes(1)
    wrapper.unmount()
    expect(RedirectingOverlay.prototype.componentWillUnmount).toHaveBeenCalledTimes(1)
  })

Also using: