Jest spy on functionality

Question

I am swapping to Jest from Mocha, and I'm wondering if there is a way to spy on a React method. For example, let's say I have the following method in my component (ignore the sdk library, it just constructs a jQuery Ajax call):

getData() {     sdk.getJSON('/someURL').done(data => {         this.setState({data});     }); } 

Using Sinon I would test this by spying on the prototype like so:

it('should call getData', () => {     sinon.spy(Component.prototype, 'getData');     mount(<Component />);     expect(Component.prototype.getData.calledOnce).to.be.true; }); 

This would ensure code coverage without mocking the method. Is there similar functionality in Jest?

EDIT: Also, if this functionality doesn't exist, what is the next best strategy for testing API calls?

Answer 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)   }); }) 

Answer 2

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