React & Enzyme:为什么beforeEach()不工作？

Question

我正在编写我的第一个React测试，结果遇到了beforeEach语句无法工作的问题。下面是我的测试文件：

import React from 'react';
import { shallow } from 'enzyme';
import Home from '../components/Home';
import IntroText from '../components/IntroText';
import Form from '../components/Form';

describe('<Home />', () => {
  beforeEach(() => {
    const wrapper = shallow(<Home />);
  });

  it('renders the IntroText component', () => {
    expect(wrapper.find(IntroText).length).toBe(1);
  });

  it('renders the Form component', () => {
    expect(wrapper.find(Form).length).toBe(1);
  });
});

下面是我的package.json的相关部分

"devDependencies": {
  "babel-jest": "^18.0.0",
  "babel-preset-es2015": "^6.22.0",
  "babel-preset-react": "^6.23.0",
  "jest": "^18.1.0",
  "react-scripts": "0.9.0",
  "react-test-renderer": "^15.4.2"
 },
"dependencies": {
  "enzyme": "^2.7.1",
  "jest-enzyme": "^2.1.2",
  "react": "^15.4.2",
  "react-addons-test-utils": "^15.4.2",
  "react-dom": "^15.4.2",
  "react-router": "^3.0.2"
},
"scripts": {
  "start": "react-scripts start",
  "build": "react-scripts build",
  "test": "react-scripts test --env=jsdom",
  "eject": "react-scripts eject"
}

当测试运行时，我得到这个错误：

ReferenceError: wrapper is not defined

我遗漏了什么？

Answer 1

您在beforeEach作用域中定义了包装器const，将其移到外部，如下所示：

import React from 'react';
import { shallow } from 'enzyme';
import Home from '../components/Home';
import IntroText from '../components/IntroText';
import Form from '../components/Form';

describe('<Home />', () => {
  let wrapper;
  beforeEach(() => {
    wrapper = shallow(<Home />);
  });

  it('renders the IntroText component', () => {
    expect(wrapper.find(IntroText).length).toBe(1);
  });

  it('renders the Form component', () => {
    expect(wrapper.find(Form).length).toBe(1);
  });
});

这样，您就可以访问it作用域内的包装器。

常量是块范围的，与使用Let语句定义的变量非常相似。常量的值不能通过重新赋值来更改，也不能重新声明。

由于您希望在beforeEach范围内分配变量并在it范围内使用它，因此必须在一个公共范围内声明该变量，在本例中就是describe范围。

补充道(适用于摩卡，但不适用于jest):

另一种可能的解决方法是使用this关键字(如果使用mocha...不能与jest一起工作)。

import React from 'react';
import { shallow } from 'enzyme';
import Home from '../components/Home';
import IntroText from '../components/IntroText';
import Form from '../components/Form';

describe('<Home />', function() {
  beforeEach(function() {
    this.wrapper = shallow(<Home />);
  });

  it('renders the IntroText component', function() {
    expect(this.wrapper.find(IntroText).length).toBe(1);
  });

  it('renders the Form component', function() {
    expect(this.wrapper.find(Form).length).toBe(1);
  });
});