javascript - useEffect 钩子(Hook)没有被 jest.spyOn mock

Question

我是 React Hooks 的新手，我想要实现的是测试一个 React 组件(称为 CardFooter)，该组件包含对 useEffect 钩子(Hook)的调用，该钩子(Hook)被触发，全局上下文变量被修改。

CardFooter.js:

const CardFooter = props => {
  const [localState, setLocalState] = useState({
    attachmentError: false
  });
  const globalContext = useContext(GlobalContext);
  React.useEffect(()=> {
    setLocalState({
    ...localState,
    attachmentError: globalContext.data.attachmentError
  });
 },[globalContext.data.attachmentError]);
}

CardFooter.test.js:

import Enzyme, { shallow } from 'enzyme';    
Enzyme.configure({ adapter: new Adapter() });
describe('<CardFooter  />', () => {
  let useEffect;
  const mockUseEffect = () => {
    useEffect.mockImplementation(f => f());
  };

  useEffect = jest.spyOn(React, "useEffect");
  mockUseEffect(); //

  it('should render correctly with no props.', () => {
  }

  const mockUseEffect = () => {
    useEffect.mockImplementation(f => f());
  };

  useEffect = jest.spyOn(React, "useEffect");
  mockUseEffect();

  const wrapper = shallow(<CardFooter />);
  expect(toJson(wrapper)).toMatchSnapshot();

});

我在运行测试时遇到的错误是:

TypeError: Cannot read property 'attachmentError' of undefined

我尝试了这里介绍的方法:https://medium.com/@pylnata/testing-react-functional-component-using-hooks-useeffect-usedispatch-and-useselector-in-shallow-9cfbc74f62fb .然而，shallow 似乎没有选择模拟的 useEffect 实现。我还尝试模拟 useContext 和 globalContext.data.attachmentError。似乎没有任何效果。

Answer 1

试试这个。注意“jest.spyOn”被放置在“beforeEach”里面

  beforeEach(() => {
    jest.spyOn(React, "useEffect").mockImplementationOnce(cb => cb()());
    
     // .... other things ....
  }