How can I use Jest to spy on a method call?

by

The key is using jests spyOn method on the object’s prototype. It should be like this:

const spy = jest.spyOn(Component.prototype, 'methodName');
const wrapper = mount(<Component {...props} />);
wrapper.instance().methodName();
expect(spy).toHaveBeenCalled();

As found here e.g.: Test if function is called react and enzyme

Please note it is also best practice to clear the spied function after each test run

let spy

afterEach(() => {
  spy.mockClear()
})

https://facebook.github.io/jest/docs/en/jest-object.html#jestclearallmocks

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