Installing Jest for Testing in Your Vite-React TypeScript Project. A Step-by-Step Guide.

Introduction

Application testing is an important aspect of web development. It helps eliminate bugs before these applications are pushed out to the users. Testing applications also helps in maintaining and refactoring code, especially in collaborative projects where a developer makes a change that is out of context thereby promoting good collaboration among teammates. It also ensures the code quality and correctness. The aim of the article is to show how unit testing is done in a react-vite app with Jest. From the setup, down to the implementation.

Jest

To know more about Jest as a testing framework, visit jest website

Prerequisite

To get started, we will need the following:

PC and a text editor. (Just kidding, of course, we already have that)
npm or yarn installed

We will start by creating a react app with Vite then we proceed to set up Jest for the testing and try out some tests on the react components.

Use Case

Step 1: Creating the react app with Vite

Open the terminal in your text editor (For the project, we will be making use of the VSCode) and proceed to create the react app using the command below: npm create vite@latest Follow the wizard and select the desired options

Vite create react app From the above, you'd see we have selected React and Typescript, and we called the project "mini-app-testing" so we will be building with Typescript.

Now run the following commands to get started and install the needed packages, step by step.

cd mini-app-testing - to navigate to the project directory.

npm install - to install the packages. (You can also use yarn but we started with npm so we stick with it).

npm run dev - to start the project.

If you have done the above correctly, you should have something like this On your VSCode App created and installation completed

On your browser The live server

Step 2: Setting up Jest

Before we dive into the process, note that Vite has certain limitations with Jest which makes setting up Jest in a Vite application to seem a bit complicated. Follow the process below to get started

npm install jest --save-dev
npm install @testing-library/react --save-dev
npm install ts-jest @types/jest --save-dev
In the package.json, add "test": jest to the script

// package.json

{
  "name": "mini-app-testing",
  "private": true,
  "version": "0.0.0",
  "type": "module",
  "scripts": {
    "dev": "vite",
    "build": "tsc && vite build",
    "lint": "eslint src --ext ts,tsx --report-unused-disable-directives --max-warnings 0",
    "test": "jest"
  },

run npm run test and you receive a message saying no test found as seen below.

No test feedback on terminal

So to fix the above, In the src folder, we create a folder called tests and add the test file: src/ tests /App.spec.tsx.

Test file structure

Add a simple test in the test file: App.test.tsx

// src/__ tests __/App.test.tsx

test('demo', () => {
  expect(true).toBe(true)
})

Run the npm run test again. Voila!!! our first test passed

Successful test run

Step 3: Testing the components

To test the components, we import the App.tsx into the App.test.tsx and run a simple truthy test on the App component.

// src/__ tests __/App.test.tsx

import { render } from "@testing-library/react"
import App from "../App"

test('demo', () => {
    expect(true).toBe(true)
})

test("Renders the main page", () => {
    render(<App />)
    expect(true).toBeTruthy()
})

Let test again, run npm run test. But it will fail due to missing dependencies and configurations as seen below. So it has to be configured to be able to import and read imported components.

Error message

Run npm install ts-node @testing-library/jest-dom --save-dev
Run npm install jest-environment-jsdom
Run npm install identity-obj-proxy --save-dev
In your root directory, create a jest.config.ts file and add the following to it

// jest.config.ts

export default {
    preset: 'ts-jest',
    testEnvironment: 'jest-environment-jsdom',
    transform: {
        "^.+\\.tsx?$": "ts-jest" 
    // process `*.tsx` files with `ts-jest`
    },
    moduleNameMapper: {
        '\\.(gif|ttf|eot|svg|png)$': '<rootDir>/test/__ mocks __/fileMock.js',
    },
}

In the src folder, create a test folder, then create a mocks folder in the test folder and add a fileMock.js file: src/test/ mocks /fileMock.js and add the following content:

// src/test/__ mocks __/fileMock.js

module.exports = {
    __esModule: true,
    default: 'test-file-stub',
};

In the App.test.tsx, import @testing-library/jest-dom

// src/__ tests __/App.test.tsx

import '@testing-library/jest-dom'
import { render } from "@testing-library/react"
import App from "../App"

test('demo', () => {
    expect(true).toBe(true)
})

test("Renders the main page", () => {
    render(<App />)
    expect(true).toBeTruthy()
})

Then run the npm run test to check if all issues have been resolved.

Import Setup successful

You can go ahead with your testing process. Happy testing!!!😀

Conclusion

In summary, incorporating Jest and installing the essential Jest packages in a React Vite application is a simple and uncomplicated process. By following a series of straightforward steps, developers can seamlessly integrate Jest into their projects and harness its robust testing features. With Jest successfully implemented, they can confidently create tests to guarantee the quality and accuracy of their React Vite applications.