Jest mocked spy function, not being called in test

Found great help from the answer here: Jest spyOn function called

This was the important step I was missing:

const instance = wrapper.instance()const spy = jest.spyOn(instance, 'yearOnChange')

Updated working test with 2 working expects.

it('yearOnChange method is called', function() {    const instance = wrapper.instance();  // <-- Needed to do this here    const spy = jest.spyOn(instance, 'yearOnChange');  // <-- Then use instance here    wrapper.instance().forceUpdate();        const event = {        target: {            value: '1999'        }    };    wrapper.instance().yearOnChange(event);    wrapper.simulate('change', event);    const result = wrapper.state('year');    console.log('result', result); // result = 1999    expect(result).toEqual('1999');    expect(spy).toHaveBeenCalled();});

You are spying and calling yearOnChange manually.

Try not calling wrapper.instance().yearOnChange(event);

Call the wrapper.instance().onChange event, or like you did, run the simulate('change') will be enough.

You could also try VehiclePicker.prototype.yearOnChange = jest.fn()

expect(VehiclePicker.prototype.yearOnChange).toBeCalled();