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Dantis Mai
Dantis Mai

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Configuration for JavaScript Testing Framework

Testing framework

Besides development, testing plays an important role, it helps us to make sure any developed feature works as expected. Especially in the refactoring codebase process, the business has to be the same, so we just basically go through all the test cases without changing them. If all of them are passed, our new codebase is good to go.

There are a lot of testing framework for Javascript (JS), which has thier own strength and weakness. Please take a look on this Comparing JS testing framework to find one. In this post I will use Jest.


My configuration

I use the configuration below in most of my Typescript projects. Because there are some important parts, I will explant them later, but for others, you can search in configuration files

import path from 'path';
const rootDirector = path.resolve(__dirname);

export default {
  clearMocks: true,
  collectCoverage: true,
  coverageDirectory: 'coverage',
  coverageProvider: 'v8',
  coverageThreshold: {
    global: {
      branches: 70,
      function: 80,
      lines: 80,
      statements: 80,
  globals: {
    'ts-jest': {
      tsconfig: path.resolve(__dirname, 'tsconfig.json'),
  moduleDirectories: ['node_modules'],
  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json', 'node'],
  moduleNameMapper: {
    '@server(.*)$': `${rootDirector}/src$1`,
    '@config(.*)$': `${rootDirector}/src/config$1`,
    '@tests(.*)$': `${rootDirector}/__tests__$1`,
    '@domain(.*)$': `${rootDirector}/src/domain$1`,
    '@controller(.*)$': `${rootDirector}/src/controller$1`,
    '@middleware(.*)$': `${rootDirector}/src/middleware$1`,
  reporters: [
      path.resolve(__dirname, 'node_modules', 'jest-html-reporter'),
        pageTitle: 'Demo test Report',
        outputPath: 'test-report.html',
  rootDir: rootDirector,
  roots: [rootDirector],
  setupFilesAfterEnv: [`${rootDirector}/__tests__/setup.ts`],
  testPathIgnorePatterns: [
  transform: {
    '^.+\\.ts$': 'ts-jest',
  testRegex: ['((/__tests__/.*)|(\\.|/)(test|spec))\\.tsx?$'],
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To use

  • Yup, first step is always installing the package, we can use the below command to do it. Besides, we are going to setup Jest config for TS project, so remember to install ts-test also.
#For npm
npm install --save-dev jest ts-jest

#For yarn
yarn add --dev jest ts-jest
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  • Create a file jest.config.ts or jest.config.js at the root level, and copy the configuration above to this file.
  • Add a script "test": "jest" to scripts in our package.json. By default, without the flag --config, jest will search in root level for the configuration file, otherwise, we need to evaluate value for --config, and also update options in the config, like ts-jest, reporters, and so on.
# Root level
"scripts": {
    "test": "jest",

# With config flag
"scripts": {
    "test": "jest --config='./jest-config/jest.config.ts'",
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  • Importing Path module: the module helps us navigate directory easier. In case we let jest.config.ts in other folder, let say jest-config:
    • <rootDir> in this case is the directory that we put in flag --config, so now the value for setupFilesAfterEnv must be ['<rootDir>/../__tests__/setup.ts']
    • if we use path module, rootDirector will point to root level.
#Without path module
setupFilesAfterEnv: [`<rootDir>/../__tests__/setup.ts`]

#With path module
setupFilesAfterEnv: [`${rootDirector}/__tests__/setup.ts`]
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  • globals: because Jest can't undestand TS, we need to install additional module ts-test, and also define ts-test config in this option.
  • moduleNameMapper: in the post tsconfig.json, I use module-alias to simlify importing modules, so I need to register those mappings again.
  • transform: it is the place for us to define pattern filename for each testing framework. In my config, I just use ts-test to test my TS modules.
  • testRegex: this option is used to let Jest know how our test files look like, where they are.

To be honest, Mock is the most important term in testing. If you want to follow developer journey, I suggest you fully understand this term

I hope this post helps you with config testing environment for your project. I am really happy to receive your feedback on this article. Thanks for your precious time reading this.

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