Jest and Enzyme Testing with TypeScript

This is an example (for reference purposes) on how to use Jest and Enzyme to test React.JS 16.x component developed in TypeScript 2.x.

Jest is a decent unit testing option which provides great TypeScript support.

Getting Started

1. Clone this repo:

git clone https://github.com/cedrickchee/react-typescript-jest-enzyme-testing react-typescript
cd react-typescript

2. Install project dependencies:

yarn

# If you are using NPM
npm install

3. Start Jest to run tests:

# start Jest in watch mode
yarn test -- --watch

# or if you are using NPM
npm t -- --watch

4. There is no step 4. You can start developing your React component and write unit test along the way.

Project

How's this project was created? From a clean project setup, here are the steps to recreate this example:

• Step 0: Pre-requisite

Install React.JS and TypeScript:

yarn add react react-dom typescript

# or if you are using NPM
npm i react react-dom typescript

• Step 1: Install Jest

Install the following using yarn/npm:

yarn add jest @types/jest ts-jest --dev

# or if you are using NPM
npm i jest @types/jest ts-jest -D

Explanation:

• Install Jest framework (jest).

• Install the types for Jest (@types/jest).

• Install the TypeScript preprocessor for Jest (ts-jest) which allows jest to transpile TypeScript on the fly and have source-map support built in.

• Save all of these to your dev dependencies (testing is almost always a npm dev-dependency).

• Step 2: Configure Jest

Add the following jest.config.js file to the root of your project:

module.exports = {
  "roots": [
    "<rootDir>/src"
  ],
  "transform": {
    "^.+\\.tsx?$": "ts-jest"
  },
  "testRegex": "(/__tests__/.*|(\\.|/)(test|spec))\\.tsx?$",
  "moduleFileExtensions": [
    "ts",
    "tsx",
    "js",
    "jsx",
    "json",
    "node"
  ],
}

Explanation:

• We always recommend having all TypeScript files in a src folder in your project. We assume this is true and specify this using the roots option.

• The transform config just tells Jest to use ts-jest for ts / tsx files.

• The testRegex tells Jest to look for tests in any __tests__ folder AND also any files anywhere that use the (.test|.spec).(ts|tsx) extension e.g. checkbox.test.tsx etc.

• The moduleFileExtensions tells Jest to recognize our file extensions. This is needed as we add ts/tsx into the defaults (js|jsx|json|node).

• Step 3: Run tests

Run npx jest --watch (or ./node_modules/.bin/jest --watch) from your project root and Jest will execute any tests you have.

Optional: Add script target for npm scripts

Add this in package.json:

{
  "test": "jest --watch"
}

• This allows you to run the tests in watch mode with a simple yarn test or npm t.

• Step 4: Setup Enzyme

Enzyme allows you to test React components with DOM support. There are three steps to setting up Enzyme:

1. Install Enzyme, types for Enzyme, a better snapshot serializer for Enzyme, enzyme-adapter-react for your React version:

yarn add enzyme @types/enzyme enzyme-to-json enzyme-adapter-react-16 --dev

# or if you are using NPM
npm i enzyme @types/enzyme enzyme-to-json enzyme-adapter-react-16 -D

2. Add "snapshotSerializers" and "setupTestFrameworkScriptFile" to your jest.config.js:

module.exports = {
  // ... ... ... TRUNCATED. Other parts as before ... ... ...

  // Setup Enzyme
  "snapshotSerializers": ["enzyme-to-json/serializer"],
  "setupTestFrameworkScriptFile": "<rootDir>/src/setupEnzyme.ts",
}

3. Create src/setupEnzyme.ts file.

import { configure } from 'enzyme';
import EnzymeAdapter from 'enzyme-adapter-react-16';

configure({ adapter: new EnzymeAdapter() });

That's all to it!