file2.test.js

describe('on user click', () => {
  const props = {
    friends,
    onUserChange: jest.fn(),
  };
  
  it('calls on user change', () => {
     const wrapper = shallow(<FriendsList {…props} />);
     wrapper.find('FriendItem[value="Paul"]').simulate('click'); 
     expect(onUserChange).toBeCalledWith('Paul');
  });
});