react-native-testing-library：如何使用 act 测试 useEffect

Question

我正在使用 react-native-testing-library 来测试我的 react-native 组件。 我有一个组件（为了这篇文章的目的，它已经被过度简化了）：

export const ComponentUnderTest = () => {

 useEffect(() => {
   __make_api_call_here_then_update_state__
 }, [])

 return (
   <View>
     __content__goes__here
   </View>
 )
} 

这是我的（简化版）component.spec.tsx：

import { render, act } from 'react-native-testing-library';
import { ComponentUnderTest } from './componentundertest.tsx';

test('it updates content on successful call', () => {
   let root;
   act(() => {
      root = render(<ComponentUnderTest />); // this fails with below error message
   });    
   expect(...);
})

现在当我运行这段代码时，我得到了这个错误： Can't access .root on unmounted test renderer

我什至现在都不知道这个错误消息是什么意思。我按照react-native-testing-library 中的文档了解如何使用act and useEffect 进行测试。

任何帮助将不胜感激。谢谢

Answer 1

我找到了解决方法：

import { render, waitFor } from 'react-native-testing-library';
import { ComponentUnderTest } from './componentundertest.tsx';

test('it updates content on successful call', async () => {
   const root = await waitFor(() =>
       render(<ComponentUnderTest />);
   );   
   expect(...);
})

Answer 2

root = render(<ComponentUnderTest />);

应该是

 root = create(<ComponentUnderTest />);

----全码sn-p。经过上述更改后它对我有用

import React, { useState, useEffect } from 'react'
import { Text, View } from 'react-native'
import { render, act } from 'react-native-testing-library'
import { create } from 'react-test-renderer'

export const ComponentUnderTest = () => {
  useEffect(() => {}, [])

  return (
    <View>
      <Text>Hello</Text>
    </View>
  )
}

test('it updates content on successful call', () => {
  let root
  act(() => {
    root = create(<ComponentUnderTest />) 
  })
})

Answer 3

您可以使用：@testing-library/react-native

例子：

import { cleanup, fireEvent, render, debug, act} from '@testing-library/react-native'

afterEach(() => cleanup());

test('given correct credentials, gets response token.', async () => {
    const { debug, getByPlaceholderText, getByRole } = await render(<Component/>);

    await act( async () => {
            const emailInput = getByPlaceholderText('Email');;
            const passwordInput = getByPlaceholderText('Password');
            const submitBtn = getByRole('button', {name: '/submitBtn/i'});

            fireEvent.changeText(emailInput, 'email');
            fireEvent.changeText(passwordInput, 'password');
            fireEvent.press(submitBtn);
    });
});

也应该与 useEffect 一起使用，但我自己还没有测试过。与 useState 一起工作正常。

Answer 4

以下步骤解决了我的情况：

• 升级React 和react-test-renderer 版本到16.9 或更高版本，支持act 内部的async 函数（据我所知，这两个包需要是相同的版本）

  李>

• 按照@helloworld 的建议，将react-native-testing-library 的render 替换为react-test-renderer 的create（谢谢您，先生，它帮助了我）

• 创建测试函数async，在act 前面加上await，并传递一个async 函数给它

最终结果如下所示：

test('it updates content on successful call', async () => {
  let root
  await act(async () => {
    root = create(<ComponentUnderTest />) 
  })
})

Answer 5

我使用useEffect 测试异步组件并触发setState 重新渲染的方法是正常设置测试用例，但使用waitFor or findBy 阻止断言，直到组件使用获取的重新渲染数据。

这是一个简单的可运行示例：

import React, {useEffect, useState} from "react";
import {FlatList, Text} from "react-native";
import {render} from "@testing-library/react-native";

const Posts = () => {
  const [posts, setPosts] = useState(null);

  useEffect(() => {
    const url = "https://jsonplaceholder.typicode.com/posts";
    fetch(url).then(res => res.json()).then(setPosts);
  }, []);

  return !posts ? <Text>loading</Text> : <FlatList
    testID="posts"
    data={posts}
    renderItem={({item: {id, title}, index}) =>
      <Text testID="post" key={id}>{title}</Text>
    }
  />;
};

describe("Posts", () => {
  beforeEach(() => {
    global.fetch = jest.fn(url => Promise.resolve({
      ok: true,
      status: 200,
      json: () => Promise.resolve([
        {id: 1, title: "foo title"},
        {id: 2, title: "bar title"},
      ])
    }));
  });

  it("should fetch posts", async () => {
    const {findAllByTestId} = render(<Posts />);
    const posts = await findAllByTestId("post", {timeout: 500});
    expect(posts).toHaveLength(2);
    expect(posts[0]).toHaveTextContent("foo title");
    expect(posts[1]).toHaveTextContent("bar title");
    expect(fetch).toHaveBeenCalledTimes(1);
  });
});

这并没有给我任何act 警告，但我已经分享了这些警告。 This open GitHub issue 似乎是规范资源。

使用的包：

{
  "dependencies": {
    "react": "^17.0.2",
    "react-dom": "^17.0.2",
    "react-native": "^0.64.0",
    "react-native-web": "^0.15.6"
  },
  "devDependencies": {
    "@babel/core": "^7.13.15",
    "@testing-library/jest-native": "^4.0.1",
    "@testing-library/react-native": "^7.2.0",
    "babel-jest": "^26.6.3",
    "jest": "^26.6.3",
    "metro-react-native-babel-preset": "^0.65.2",
    "react-test-renderer": "^17.0.2"
  }
}

在 Jest 配置中：

setupFilesAfterEnv: ["@testing-library/jest-native/extend-expect"],

对于.toHaveTextContent 匹配器。或者您可以使用导入：

import "@testing-library/jest-native/extend-expect";