在 React 组件之外测试 mousedown 事件：Jest + Enzyme

Question

我想使用 Jest 和 Enzyme 编写一个测试来测试具有事件侦听器的组件，这样当给定 html 元素之外发生 mousedown 事件时，就会发生更改（在本示例中，状态值被切换） .我正在使用 jest 来模拟事件侦听器并模拟 mousedown 事件，但是，当我尝试运行此测试时，我收到以下错误消息：

TypeError：无法在“节点”上执行“包含”：参数 1 不是“节点”类型。

显然，当我使用map.mousedown({ target: <section /> }); 模拟 mousedown 事件时，我认为<div /> 不是我应该提供的正确值。如何正确模拟在我的组件之外发生的 mousedown 事件？你可以看到下面的代码。谢谢！

sampleComponent.jsx：

import * as React from 'react';

const SampleComponent = () => {
  const [state, setState] = React.useState(false);
  const ref = React.useRef(null);

  const handleClickOutside = (event) => {
    if (
      !ref.current.contains(event.target)
    ) {
      setState(true);
    }
  };

  React.useEffect(() => {
    document.addEventListener('mousedown', handleClickOutside);
    return () => document.removeEventListener('mousedown', handleClickOutside);
  });

  return (
    <div
      id="sample-div"
      ref={ref}
    >
      {`State value is: ${state}`}
    </div>
  );
};

export default SampleComponent;

sampleComponent.test.jsx：

import * as React from 'react';
import { mount } from 'enzyme';
import SampleComponent from './sampleComponent';

const setup = () => mount(<SampleComponent />);

test('testing mousedown', () => {
  const map = {};
  document.addEventListener = jest.fn((event, callback) => {
    map[event] = callback;
  });
  const wrapper = setup();
  expect(wrapper.find('#sample-div').text()).toBe('State value is: false');
  map.mousedown({ target: <section /> });
  expect(wrapper.find('#sample-div').text()).toBe('State value is: true');
});

Answer 1

您不能将 react JSX 作为 event.target 的值传递。由于您使用document.addEventListener，因此它是本机 DOM 事件。你需要传递一个原生 DOM，比如document.createElement('a')。

这是您的示例的测试用例：

sampleComponent.tsx:

import React from 'react';

const SampleComponent = () => {
  const [state, setState] = React.useState(false);
  const ref = React.useRef(null);

  const handleClickOutside = event => {
    if (!(ref.current as any).contains(event.target)) {
      setState(true);
    }
  };

  React.useEffect(() => {
    document.addEventListener('mousedown', handleClickOutside);
    return () => document.removeEventListener('mousedown', handleClickOutside);
  });

  return (
    <div id="sample-div" ref={ref}>
      {`State value is: ${state}`}
    </div>
  );
};

export default SampleComponent;

sampleComponent.test.tsx:

import React from 'react';
import { mount } from 'enzyme';
import SampleComponent from './sampleComponent';
import { act } from 'react-dom/test-utils';

const setup = () => mount(<SampleComponent />);

beforeEach(() => {
  jest.resetAllMocks();
});
test('testing mousedown - 1', () => {
  const map: any = {};
  document.addEventListener = jest.fn((event, callback) => {
    map[event] = callback;
  });
  const wrapper = setup();
  expect(wrapper.find('#sample-div').text()).toBe('State value is: false');
  act(() => {
    map.mousedown({ target: document.createElement('a') });
  });
  expect(wrapper.find('#sample-div').text()).toBe('State value is: true');
  expect(document.addEventListener).toBeCalledTimes(2);
});

test('testing mousedown - 2', () => {
  const map: any = {};
  document.addEventListener = jest.fn((event, callback) => {
    map[event] = callback;
  });
  const wrapper = setup();
  expect(wrapper.find('#sample-div').text()).toBe('State value is: false');
  act(() => {
    map.mousedown({ target: wrapper.getDOMNode() });
  });
  expect(wrapper.find('#sample-div').text()).toBe('State value is: false');
  expect(document.addEventListener).toBeCalledTimes(1);
});

100% 覆盖率的单元测试结果：

PASS  src/stackoverflow/58610112/sampleComponent.test.tsx (8.041s)
  ✓ testing mousedown - 1 (46ms)
  ✓ testing mousedown - 2 (3ms)

---------------------|----------|----------|----------|----------|-------------------|
File                 |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
---------------------|----------|----------|----------|----------|-------------------|
All files            |      100 |      100 |      100 |      100 |                   |
 sampleComponent.tsx |      100 |      100 |      100 |      100 |                   |
---------------------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        9.5s