End-to-End Testing with Node.js

End-to-End (E2E) testing is like walking through your application as a user would. It helps you ensure that everything works together as expected. In this tutorial, we'll set up E2E testing for a Node.js application using Jest and Puppeteer. Let’s get started!

Creating a New Node.js Project

First, we'll create a new directory for our project and initialize a new Node.js project.

Open your terminal and run the following commands:

mkdir e2e-testing
cd e2e-testing
npm init -y

This will create a new directory named e2e-testing and initialize a Node.js project inside it.

Installing Express

Next, we'll install Express, a popular Node.js framework for building web applications.

npm install express

Creating a Simple Express Server

Now, let's create a simple Express server. Create a file named app.js and add the following code:

const express = require('express');
const app = express();
const port = 3000;

app.get('/', (req, res) => {
  res.send('Hello, world!');
});

app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`);
});

This code sets up a basic server that responds with "Hello, world!" when you visit the root URL.

Running Your Server

Run your server by executing the following command in your terminal:

node app.js

You should see a message saying Example app listening at http://localhost:3000. Open your browser and navigate to http://localhost:3000 to see the message.

Installing Jest and Puppeteer

We need Jest for our testing framework and Puppeteer to control a headless browser for our E2E tests.

npm install --save-dev jest puppeteer

Configuring Jest

We'll configure Jest to use Puppeteer. In your package.json file, add the following Jest configuration:

"scripts": {
  "test": "jest"
},
"jest": {
  "preset": "jest-puppeteer"
}

Installing Jest-Puppeteer Preset

We need to install the Jest-Puppeteer preset to integrate Jest with Puppeteer seamlessly.

npm install --save-dev jest-puppeteer

Creating a Jest Configuration File

Create a file named jest-puppeteer.config.js with the following content:

module.exports = {
  launch: {
    headless: true, // set to false if you want to see the browser while testing
  },
};

This configuration tells Puppeteer to run in headless mode (without a visible browser).

Creating a Test Directory

Create a directory named tests to store our test files.

mkdir tests

Creating a Test File

Inside the tests directory, create a file named app.test.js and add the following code:

const puppeteer = require('puppeteer');

describe('App', () => {
  let browser;
  let page;

  beforeAll(async () => {
    browser = await puppeteer.launch();
    page = await browser.newPage();
  });

  afterAll(async () => {
    await browser.close();
  });

  test('should display "Hello, world!" on the home page', async () => {
    await page.goto('http://localhost:3000');
    await page.waitForSelector('body');
    const text = await page.$eval('body', (e) => e.textContent);
    expect(text).toContain('Hello, world!');
  });
});

Running Your Test

Run your test by executing the following command:

npm test

Jest will start Puppeteer, open a browser, navigate to http://localhost:3000, and check if the text "Hello, world!" is present on the page. If everything is set up correctly, the test should pass.

Advanced Testing

Now, let's add more functionality to our application and write tests for it.

Update Your Express Server

Modify app.js to include a simple form that greets the user:

const express = require('express');
const app = express();
const port = 3000;

app.use(express.urlencoded({ extended: true }));

app.get('/', (req, res) => {
  res.send(`
    <form action="/greet" method="post">
      <input type="text" name="name" placeholder="Enter your name" />
      <button type="submit">Submit</button>
    </form>
  `);
});

app.post('/greet', (req, res) => {
  const name = req.body.name;
  res.send(`Hello, ${name}!`);
});

app.listen(port, () => {
  console.log(`Example app listening at http://localhost:${port}`);
});

Writing a Test for the Form

Add a new test in app.test.js:

test('should submit the form and display a greeting', async () => {
  await page.goto('http://localhost:3000');
  await page.type('input[name=name]', 'John');
  await page.click('button[type=submit]');
  await page.waitForSelector('body');
  const text = await page.$eval('body', (e) => e.textContent);
  expect(text).toBe('Hello, John!');
});

Running Your Tests Again

Run your tests by executing the command:

npm test

Puppeteer will open the form, type a name into the input field, submit the form, and check if the greeting message is displayed correctly.

Conclusion

You've successfully set up and run End-to-End tests for a Node.js application using Jest and Puppeteer! We covered: