1. 从后端结构到测试入门

Project structure

将日志记录提取到单独的模块

新建文件夹utils, 新建文件logger.js

const info = (...params) => {
  console.log(...params);
}
const error = (...params) => {
  console.error(...params)
}
module.exports = {
  info, error
}

exercise 4.1-4.2

创建一个bloglist应用
npm init 初始化
npm install express
npm install —save-dev nodemon
在scripts添加 “dev”:”nodemon index.js”
npm install cors
npm install mongoose
npm install dotenv

Testing Node applications

Jest 是一个由 Facebook 内部开发和使用的测试库，它可以很好地测试后端，并且在测试 React 应用时表现出色。 (Windows 用户: 如果项目目录的路径所包含的目录名称含有空格， Jest 可能无法工作。)

安装Jest为开发依赖：

npm install --save-dev jest

修改package.json中的scripts中的test, 以verbose样式报告测试执行情况：

"test": "jest --verbose"

在package.json末尾添加如下内容，指定jest执行环境为node

"jest": {
  "testEnvironment": "node"
}

在utils文件夹创建for_testing.js文件

const palindrome = (string) => {
  return string
    .split('')
    .reverse()
    .join('')
}
const average = (array) => {
  const reducer = (sum, item) => {
    return sum + item
  }
  return array.length === 0 ? 0 : array.reduce(reducer, 0) / array.length
}
module.exports = {
  palindrome,
  average
}

新建tests文件夹
新建palindrome.test.js文件(Jest 默认情况下希望测试文件的名称包含 .test. )

const palindrome = require('../utils/for_testing').palindrome
test('palindrome of a', () => {
  const result = palindrome('a')
  expect(result).toBe('a')
})
test('palindrome of react', () => {
  const result = palindrome('react')
  expect(result).toBe('tcaer')
})
test('palindrome of releveler', () => {
  const result = palindrome('releveler')
  expect(result).toBe('releveler')
})

新建average.test.js文件
这里定义了describe块， 描述块可用于将测试分组为逻辑集合。

const average = require('../utils/for_testing').average
describe('average', () => {
  test('of one value is the value itself', () => {
    expect(average([1])).toBe(1)
  })
  test('of many is calculated right', () => {
    expect(average([1, 2, 3, 4, 5, 6])).toBe(3.5)
  })
  test('of empty array is zero', () => {
    expect(average([])).toBe(0)
  })
})

运行命令 **npm test**，控制台会显示测试结果

exercise 4.2 - 4.7

list_helper.js

const dummy = (blogs) => {
  return 1
}
const totalLikes = (blogs) => {
  return blogs.reduce((sum, currrent) => sum + currrent.likes, 0)
}
module.exports = {
  dummy,
  totalLikes
}

list.test.js

const listHelper = require('../utils/list_helper')
describe('dummy', () => {
  test('dummy returns one', () => {
    const blogs = []
    const result = listHelper.dummy(blogs)
    expect(result).toBe(1)
  })
})
describe("totalLikes", () => {
  const listWithOneBlog = [
    {
      _id: '5a422aa71b54a676234d17f8',
      title: 'Go To Statement Considered Harmful',
      author: 'Edsger W. Dijkstra',
      url: 'http://www.u.arizona.edu/~rubinson/copyright_violations/Go_To_Considered_Harmful.html',
      likes: 5,
      __v: 0
    }
  ]
  const blogs = [
    {
      _id: "5a422a851b54a676234d17f7",
      title: "React patterns",
      author: "Michael Chan",
      url: "https://reactpatterns.com/",
      likes: 7,
      __v: 0
    },
   -- snip --
  ]
  test('when list has only one blog, equals the likes of that', () => {
    const result = listHelper.totalLikes(listWithOneBlog)
    expect(result).toBe(5)
  })
  test('a lot of blogs', () => {
    const result = listHelper.totalLikes(blogs)
    expect(result).toBe(36)
  })
})

npm test运行所有测试
npm test -- -t 'a log of blogs' 进行单个测试

如果是比较对象的值，用toEqual

const can1 = {
  flavor: 'grapefruit',
  ounces: 12,
};
const can2 = {
  flavor: 'grapefruit',
  ounces: 12,
};
describe('the La Croix cans on my desk', () => {
  test('have all the same properties', () => {
    expect(can1).toEqual(can2);
  });
  test('are not the exact same can', () => {
    expect(can1).not.toBe(can2);
  });
});

Lodash

官方文档
中文文档
Lodash 通过降低 array、number、objects、string 等等的使用难度从而让 JavaScript 变得更简单。 Lodash 的模块化方法 非常适用于：

• 遍历 array、object 和 string
• 对值进行操作和检测
• 创建符合功能的函数