删除了jest /酶测试事件监听器

Question

学习开玩笑和酶来测试应用程序，使用create-react-app启动。

在unmount之后使用shallow模拟add / removeEventListener崩溃，并在unmount之后使用mount发出警告，见下文。谁知道我做错了什么？

我的测试：

it('should add and remove resize event handler', () => {
  const adder = jest
    .spyOn(global, 'addEventListener')
    .mockImplementation(() => {});
  const remover = jest
    .spyOn(global, 'removeEventListener')
    .mockImplementation(() => {});
  const wrapper = shallow(<App />);
  // this seems to work
  expect(adder).toHaveBeenCalled();
  // causing issues
  wrapper.unmount();
  expect(remover).toHaveBeenCalled();
});

在unmount之后使用mount：

  console.error node_modules/fbjs/lib/warning.js:33
    Warning: Can only update a mounted or mounting component. This usually means you called setState, replaceState, or forceUpdate on an unmounted component. This is a no-op.

    Please check the code for the App component.

在unmount之后使用shallow：

/home/nik/projects/learn/jest/node_modules/react-scripts/scripts/test.js:20
  throw err;
  ^

Invariant Violation: ReactShallowRenderer render(): Invalid component element.
    at invariant (/home/nik/projects/learn/jest/node_modules/fbjs/lib/invariant.js:42:15)
    at ReactShallowRenderer.render (/home/nik/projects/learn/jest/node_modules/enzyme-adapter-react-16/node_modules/react-test-renderer/cjs/react-test-renderer-shallow.development.js:104:38)
    at Updater.enqueueSetState (/home/nik/projects/learn/jest/node_modules/enzyme-adapter-react-16/node_modules/react-test-renderer/cjs/react-test-renderer-shallow.development.js:329:20)
    at App.Object.<anonymous>.Component.setState (/home/nik/projects/learn/jest/node_modules/react/cjs/react.development.js:237:16)
    at loadData.then.results (/home/nik/projects/learn/jest/src/App.js:15:12)
    at <anonymous>
    at process._tickCallback (internal/process/next_tick.js:188:7)
error An unexpected error occurred: "Command failed.
Exit code: 1
Command: sh
Arguments: -c react-scripts test --env=jsdom
Directory: /home/nik/projects/learn/jest
Output:
".
info If you think this is a bug, please open a bug report with the information provided in "/home/nik/projects/learn/jest/yarn-error.log".
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Answer 1

我把承诺包裹起来

  return Promise.resolve().then(() => {
    wrapper.unmount();
    expect(remover).toHaveBeenCalled();
  });

也错过了错误的线索，'loadData' - 没有嘲笑：

  jest.spyOn(App.prototype, 'loadData')
    .mockImplementation(() => {
      return new Promise(resolve => resolve([topics, subTopics]))
    });

Answer 2

要解决第一个问题，必须采取措施避免在卸载组件后调用setState。

更简单的方法是保持_isMounted标志，你将在调用setState之前检查它：

componentDidMount() {
  this._isMounted = true;

  this.loadData().then(results => {
    if (!this._isMounted) {
      return;
    }

    const [topics, subTopics, ...rest] = results;

    this.setState({ topics, subTopics });
  });

  window.addEventListener('resize', this.someHandler);
}

componentWillUnmount() {
  this._isMounted = false;

  window.removeEventListener('resize', this.someHandler);
}

您可以阅读有关此问题的更多信息，并在React Blog中找到另一个解决方案：https://reactjs.org/blog/2015/12/16/ismounted-antipattern.html