Jest spy on functionality

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

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)
  });
})

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();
});