Run with yarn/npm

setup

config package.json

{
...
  "scripts": {
    "start": "node scripts/start.js",
    "test": "node scripts/test.js --env=jsdom",
...
}

scripts/test.js content

'use strict'

// Do this as the first thing so that any code reading it knows the right env.
process.env.BABEL_ENV = 'test'
process.env.NODE_ENV = 'test'
process.env.PUBLIC_URL = ''

// Makes the script crash on unhandled rejections instead of silently
// ignoring them. In the future, promise rejections that are not handled will
// terminate the Node.js process with a non-zero exit code.
process.on('unhandledRejection', err => {
  throw err
})

// Ensure environment variables are read.
require('../config/env')

const jest = require('jest')
const argv = process.argv.slice(2)

// Watch unless on CI or in coverage mode
if (!process.env.CI && argv.indexOf('--coverage') < 0) {
  argv.push('--watch')
}

jest.run(argv)

Notes: both package.json and files in scripts dir are generated by create-react-app CLI tool.

command line

yarn test

test single file

yarn test src/index.test.js

test without watch mode

$ yarn test index.test.js -- --watchAll=false

Ref: https://stackoverflow.com/questions/39724017/running-cra-jest-in-non-interactive-mode

Generate for all the directories

$ yarn test --coverage

Code coverage report

Use this to exclude this file in the coverage report.

/* istanbul ignore file */

test single

describe('Component', () => {
  test('Test no run', () => {
    ...
  })

  test('Test no run', () => {
    ...
  })

  test.only('Only this test run', () => {
    ...
  })
})

or

yarn test src/index.test.jsx

compare object vs primitive value

expect({foo:'bar'}).toEqual({foo:'bar'}) // object
expect(1).toBe(1) // primitive value

Configurations vs CLI Options

Configurations (https://jestjs.io/docs/configuration) CLI Options (https://jestjs.io/docs/cli) In file Default Value
"collectCoverage": true –coverage=true or –coverage or –collectCoverage … false
"testEnvironment": "jsdom" --env=jsdom jest-env “node”

References