单元测试之文件模块

安装jest

yarn add --dev jest

将下面的配置部分添加到你的package.json 里面：

{
  "scripts": {
    "test": "jest"
  }
}

创建文件目录的规则

├── __tests__
│   └── component.spec.js # test
│   └── anything # test
├── package.json # not test
├── foo.test.js # test
├── bar.spec.jsx # test
└── component.js # not test

创建测试文件(如何改写模块)

const db = require('../db.js')
const fs = require('fs')
jest.mock('fs') // 必须添加，改写的假fs模块

describe('db', () => {
    afterEach(() => {
        fs.clearMocks()
    })
    it('can read', async () => {
        const data = [{ title: 'hi', done: true }]
        fs.setReadFileMock('/xxx', null, JSON.stringify(data))
        const list = await db.read('/xxx')
        expect(list).toStrictEqual(data)   // 严格相等
    })
    it('can write', async () => {
        let fakeFile
        fs.setWriteFileMock('/yyy', (path, data, callback) => {
            fakeFile = data
            callback(null)
        })
        const list = [{ title: '见欧阳娜娜', done: true }, { title: '见迪丽热巴', done: true }]
        await db.write(list, '/yyy')
        expect(fakeFile).toBe(JSON.stringify(list) + '\n')
    })
})

如何测试写文件

const fs = jest.genMockFromModule('fs'); // 专门用于测试的模块
const _fs = jest.requireActual('fs'); // 导入真实的fs用的方法

Object.assign(fs, _fs)

let readMocks = {}

fs.setReadFileMock = (path, error, data) => {
    readMocks[path] = [error, data]
}

fs.readFile = (path, options, callback) => {
    if (callback === undefined) {
        callback = options
    }
    if (path in readMocks) {
        callback(...readMocks[path])
    } else {
        _fs.readFile(path, options, callback)
    }
}

let writeMocks = {}

fs.setWriteFileMock = (path, fn) => {
    writeMocks[path] = fn
}

fs.writeFile = (path, data, options, callback) => {
    if (path in writeMocks) {
        writeMocks[path](path, data, options, callback)
    } else {
        _fs.writeFile(path, data, options, callback)
    }
}

检查结果

运行命令

yarn test