单元测试:用酶反应上下文 api 返回一个空对象 [英] Unit testing: react context api with enzyme return an empty object

问题描述

我第一次尝试使用 React 上下文 API 将信息从主组件传递到孙组件.

所以首先我创建了一个上下文

const MyContext = React.createContext({});导出默认的 MyContext；

这里是设置上下文值的主要组件

从./MyContext.js"导入MyContext；从./ParentComponent.js"导入ParentComponent；功能应用(){返回 (<div><MyContext.Provider value={{ foo: 12 }}><父组件/></MyContext.Provider>

);}

父组件不关心上下文，只是在这里创建孙组件

从./ChildComponent.js"导入 ChildComponent；类父组件扩展组件{使成为() {返回 (<div>家长<子组件/>

);}}导出默认父组件；

这里是读取上下文的子组件

从./MyContext.js"导入MyContext；class ChildComponent 扩展 PureComponent {构造函数(){极好的();this.state = {酒吧:456};}使成为() {返回 (<div><MyContext.Consumer>{({ foo }) =>(<div><h1>你好，我是 ChildComponent</h1><h2>上下文值:{foo}</h2><h2>状态值:{this.state.bar}</h2><button onClick={() =>this.setState({ bar: foo })}>点击我

)}</MyContext.Consumer>

);}}导出默认子组件；

目前没有问题.一切都按预期工作.ChildComponent 已检索到上下文值.

当我尝试用笑话/酶测试它时，问题就出现了.我无法设置上下文

it(应该测试上下文值", () => {让包装器 = mount(, {上下文:{ foo: 987 }});期望(wrapper.state(bar")).toEqual(456);期望(wrapper.context(foo")).toEqual(987);});

最后一个期望失败并且上下文值是一个空对象.所以 foo 是未定义的

我在这里重现了这个问题:https://codesandbox.io/embed/x25yop4x5w?fontsize=14

感谢您的帮助

解决方案

Enzyme context 影响遗留的 React 上下文，而不是现代的上下文 API.它应该被嘲笑:

mount(<MyContext.Provider value={{foo: 987}}><ChildComponent/></MyContext.Provider>)

并断言:

expect(wrapper.find('h2').text()).toBe('Context value: 987');

I am trying for the first time to use React context API to pass information from a main component to a grandchild component.

So first I have created a context

const MyContext = React.createContext({});

export default MyContext;

Here is the main component that sets the value of the context

import MyContext from "./MyContext.js";
import ParentComponent from "./ParentComponent.js";

function App() {
  return (
    <div>
      <MyContext.Provider value={{ foo: 12 }}>
        <ParentComponent />
      </MyContext.Provider>
    </div>
  );
}

The parent component doesn't care about the context and is just here to create the grandchild component

import ChildComponent from "./ChildComponent.js";

class ParentComponent extends Component {
  render() {
    return (
      <div>
        Parent
        <ChildComponent />
      </div>
    );
  }
}

export default ParentComponent;

And here is the child component that reads the context

import MyContext from "./MyContext.js";

class ChildComponent extends PureComponent {
  constructor() {
    super();
    this.state = {
      bar: 456
    };
  }

  render() {
    return (
      <div>
        <MyContext.Consumer>
          {({ foo }) => (
            <div>
              <h1>Hello I'm the ChildComponent</h1>
              <h2>Context value: {foo}</h2>
              <h2>State value: {this.state.bar}</h2>
              <button onClick={() => this.setState({ bar: foo })}>
                Click me
              </button>
            </div>
          )}
        </MyContext.Consumer>
      </div>
    );
  }
}

export default ChildComponent;

So far no problem. Everything works as expected. The ChildComponent has retrieved the context value.

The problem comes when I try to test it with jest/enzyme. I can't manage to set the context

it("Should test the context value", () => {
  let wrapper = mount(<ChildComponent />, {
    context: { foo: 987 }
  });

  expect(wrapper.state("bar")).toEqual(456);
  expect(wrapper.context("foo")).toEqual(987);
});

The last expect fails and the context value is an empty object. So foo is undefined

I have recreated the problem here: https://codesandbox.io/embed/x25yop4x5w?fontsize=14

Thank you for your help

解决方案

Enzyme context affects legacy React context, not modern context API. It should be mocked with:

mount(<MyContext.Provider value={{foo: 987}}><ChildComponent/></MyContext.Provider>)

And asserted with:

expect(wrapper.find('h2').text()).toBe('Context value: 987');

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