It can be tempting to jump right into coding features and solely testing them by hand when you first start developing applications in Node.js. Small projects may benefit from this, but as your codebase expands, it soon becomes an issue. When you add new features, existing ones break, bugs occur, and manual testing slows down.

Test-driven development, or TDD, is useful in this situation. TDD is the process of writing a test for a feature, seeing it fail, writing the code to pass it, and then cleaning up your implementation while maintaining a green test score. This cycle pushes you to consider your code's purpose carefully before writing it.

This post will explain how to set up a Node.js project for TDD, write the initial tests, and use Jest and Supertest to create a basic API. You will have a useful workflow at the end that you may use for your own projects.

Why TDD Matters in Node.js?
Node.js is often used for building backends and APIs. These systems typically interact with databases, handle multiple requests, and address edge cases such as invalid inputs or timeouts. If you rely only on manual testing, it is very easy to miss hidden bugs.

With TDD, you get:

• Confidence that your code works as expected.
• Documentation of your intended behavior through test cases.
• Refactoring freedom, since you can change implementation details while ensuring nothing breaks.
• Fewer regressions because tests catch mistakes early.

Let us start building a small project using this approach.

Step 1. Setting Up the Project
Create a new folder for the project and initialize npm:
mkdir tdd-node-example
cd tdd-node-example
npm init -y

This creates a package.json file that will hold project metadata and dependencies.

Now install Jest, which is a popular testing framework for Node.js:
npm install --save-dev jest

Also, install Supertest, which will help us test HTTP endpoints:
npm install --save-dev supertest

To make things easier, add a test script in package.json:
{
  "scripts": {
    "test": "jest"
  }
}

This allows you to run tests with npm test.

Step 2. Writing the First Failing Test

Let us create a simple module that manages a list of tasks, similar to a basic to-do list. Following TDD, we will start with the test.

Inside a tests folder, create taskManager.test.js:
const TaskManager = require("../taskManager");

describe("TaskManager", () => {
  it("should add a new task", () => {
    const manager = new TaskManager();
    manager.addTask("Learn TDD");
    const tasks = manager.getTasks();
    expect(tasks).toContain("Learn TDD");
  });
});

We have not written taskManager.js yet, so that this test will fail. That is the point.

Run the test:
npm test

Jest will complain that ../taskManager it cannot be found. That confirms we need to write the implementation.

Step 3. Making the Test Pass
Now create taskManager.js at the root:
class TaskManager {
  constructor() {
    this.tasks = [];
  }

  addTask(task) {
    this.tasks.push(task);
  }

  getTasks() {
    return this.tasks;
  }
}

module.exports = TaskManager;

Run npm test again. This time the test passes. Congratulations, you just completed your first TDD cycle: red → green.

Step 4. Adding More Tests
Now, let us expand our tests. Modify taskManager.test.js:
const TaskManager = require("../taskManager");

describe("TaskManager", () => {
  it("should add a new task", () => {
    const manager = new TaskManager();
    manager.addTask("Learn TDD");
    expect(manager.getTasks()).toContain("Learn TDD");
  });

  it("should remove a task", () => {
    const manager = new TaskManager();
    manager.addTask("Learn Jest");
    manager.removeTask("Learn Jest");
    expect(manager.getTasks()).not.toContain("Learn Jest");
  });

  it("should return an empty list initially", () => {
    const manager = new TaskManager();
    expect(manager.getTasks()).toEqual([]);
  });
});

Now rerun the tests. The one for removeTask will fail since we have not implemented it.

Update taskManager.js:
class TaskManager {
  constructor() {
    this.tasks = [];
  }

  addTask(task) {
    this.tasks.push(task);
  }

  removeTask(task) {
    this.tasks = this.tasks.filter(t => t !== task);
  }

  getTasks() {
    return this.tasks;
  }
}

module.exports = TaskManager;

Run npm test again. All tests pass. Notice how the tests guided the implementation.

Step 5. Refactoring Safely
One beauty of TDD is that you can refactor with confidence. For example, we could change how tasks are stored internally. Maybe instead of an array, we want a Set to avoid duplicates.

Update the class
class TaskManager {
  constructor() {
    this.tasks = new Set();
  }

  addTask(task) {
    this.tasks.add(task);
  }

  removeTask(task) {
    this.tasks.delete(task);
  }

  getTasks() {
    return Array.from(this.tasks);
  }
}

module.exports = TaskManager;

Run the tests again. If they all pass, you know your refactor did not break behavior.

Step 6. Testing an API with Jest and Supertest
Unit tests are important, but most Node.js applications expose APIs. Let us use Express and Supertest to apply TDD to an endpoint.

First, install Express:
npm install express

Create app.js:
const express = require("express");
const TaskManager = require("./taskManager");

const app = express();
app.use(express.json());

const manager = new TaskManager();

app.post("/tasks", (req, res) => {
  const { task } = req.body;
  manager.addTask(task);
  res.status(201).json({ tasks: manager.getTasks() });
});

app.get("/tasks", (req, res) => {
  res.json({ tasks: manager.getTasks() });
});

module.exports = app;

Now, create a test file tests/app.test.js:
const request = require("supertest");
const app = require("../app");

describe("Task API", () => {
  it("should add a task with POST /tasks", async () => {
    const response = await request(app)
      .post("/tasks")
      .send({ task: "Write tests" })
      .expect(201);

    expect(response.body.tasks).toContain("Write tests");
  });

  it("should return all tasks with GET /tasks", async () => {
    await request(app).post("/tasks").send({ task: "Practice TDD" });

    const response = await request(app)
      .get("/tasks")
      .expect(200);

    expect(response.body.tasks).toContain("Practice TDD");
  });
});

Run npm test. Both tests should pass, confirming that our API works.

To actually run the server, create server.js:
const app = require("./app");

const PORT = 3000;
app.listen(PORT, () => {
  console.log(`Server running on port ${PORT}`);
});

Now you can try node server.js to use a tool like Postman or curl to send requests.

Step 7. Common Pitfalls in TDD
Writing too many trivial tests: Do not test things like whether 2 + 2 equals 4. Focus on meaningful business logic.

• Forgetting the cycle: Always follow the red → green → refactor cycle. Jumping ahead can lead to sloppy tests.
• Slow tests: Keep unit tests fast. If you hit a database or external API, use mocks or stubs.
• Unclear test names: Use descriptive test names that act as documentation.

Step 8. Best Practices

• Keep your tests in a separate tests folder or alongside the files they test.
• Run tests automatically before pushing code. You can set up a Git hook or CI pipeline.
• Use coverage tools to measure how much of your code is tested. With Jest, run npm test -- --coverage.
• Write tests that are independent of each other. Do not let one test rely on data from another.

Conclusion
Test-driven development with Node.js may feel slow at first, but it quickly pays off by giving you confidence in your code. By starting with a failing test, writing just enough code to pass, and then refactoring, you create a safety net that allows you to move faster in the long run. We walked through setting up Jest, writing unit tests for a TaskManager class, refactoring safely, and even testing API endpoints using Supertest. The process is the same no matter how big your application grows.

If you are new to TDD, begin small. Write a few tests for a utility function or a simple route. With practice, the habit of writing tests before code will become second nature, and your Node.js projects will be more reliable and easier to maintain.

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Most developers were unaware that Node.js would change the way web apps are created when it initially surfaced in 2009. These days, it powers anything from platforms used by millions of people globally to small personal projects. This post will examine how Node.js transformed web development, its popularity, and its implications for developers looking to create cutting-edge, quick apps.

The State of Web Development Before Node.js
Before Node.js, building web applications usually required separate technologies for the frontend and backend. The frontend ran in the browser using JavaScript, while the backend relied on languages like PHP, Java, Ruby, or Python. This separation often created friction because developers had to switch between different programming languages, ecosystems, and tools.

Backends were also synchronous by nature in most environments. Each request was processed in order, and if one operation took time, such as reading from a database, the system had to wait before moving on to the next task. This limited how many requests a server could handle at once.
What Node.js Brought to the Table

Node.js changed this picture in three big ways:

• JavaScript Everywhere: Developers could now use the same language on both the frontend and backend. This made it easier for teams to share knowledge and code.
• Non-blocking I/O: Node.js uses an event-driven, asynchronous model. This means it can handle thousands of requests at the same time without getting stuck waiting for one task to finish.
• Huge Ecosystem: The Node Package Manager (NPM) quickly became one of the largest software ecosystems in the world, with millions of packages that help developers build faster.

The Event-Driven Model Explained
At the core of Node.js is its event loop. Instead of processing requests one by one, Node.js listens for events and responds as soon as it can. This is why it is so good at handling applications that require many concurrent connections, like chat apps, live dashboards, or streaming services.

Here is a simple example:
const http = require('http');

const server = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' });
  res.end('Hello from Node.js\n');
});

server.listen(3000, () => {
  console.log('Server running at http://localhost:3000/');
});

This small script creates a working web server with just a few lines of code. Compare this to older backends, where setting up a basic server required much more boilerplate.

Asynchronous Programming in Action
Node.js relies heavily on callbacks, promises, and async/await to manage asynchronous tasks. For example, reading a file in Node.js does not block the entire application:
const fs = require('fs');

fs.readFile('data.txt', 'utf8', (err, data) => {
  if (err) {
    console.error('Error reading file:', err);
    return;
  }
  console.log('File contents:', data);
});

console.log('Reading file...');

When you run this code, “Reading file...” prints before the actual file contents. That is because Node.js starts reading the file, but does not pause the rest of the program. This makes applications more efficient.

With modern JavaScript, developers can write the same logic using async/await for cleaner code:
const fs = require('fs').promises;

async function readFile() {
  try {
    const data = await fs.readFile('data.txt', 'utf8');
    console.log('File contents:', data);
  } catch (err) {
    console.error('Error reading file:', err);
  }
}

readFile();

Real-Time Applications
One of the biggest impacts of Node.js is in real-time web applications. Before Node.js, creating a chat app or live notifications system often required hacks like long polling, which were inefficient. With Node.js and libraries like Socket.IO, developers can easily build real-time communication.

Example of a simple chat server:
const http = require('http');
const socketIo = require('socket.io');

const server = http.createServer();
const io = socketIo(server);

io.on('connection', (socket) => {
  console.log('A user connected');

  socket.on('message', (msg) => {
    console.log('Message received:', msg);
    io.emit('message', msg);
  });

  socket.on('disconnect', () => {
    console.log('User disconnected');
  });
});

server.listen(3000, () => {
  console.log('Chat server running on http://localhost:3000');
});

With just a few lines of code, you now have a chat server capable of handling multiple users at once. This ease of building real-time features is one reason Node.js became a favorite in the developer community.

The Rise of Full-Stack JavaScript
Another big change Node.js brought is the rise of the “JavaScript everywhere” philosophy. With Node.js on the backend and frameworks like React or Vue on the frontend, developers could use a single language across the entire stack. This gave birth to the role of the full-stack JavaScript developer.

Frameworks like Express.js made building web servers easier and more structured. For example:
const express = require('express');
const app = express();

app.get('/', (req, res) => {
  res.send('Welcome to my Node.js app!');
});

app.listen(3000, () => {
  console.log('App running on http://localhost:3000');
});

Express quickly became the go-to framework for Node.js applications and laid the foundation for other tools like NestJS, Fastify, and Hapi.

Microservices and Node.js
As applications grew larger, companies started moving from monolithic designs to microservices. Node.js fits perfectly into this architecture because it is lightweight, fast, and scalable. Developers could create small independent services, each handling a specific task, and connect them together.

This made it easier to scale parts of the system independently. For example, an e-commerce site might have one service for handling user authentication, another for payments, and another for product listings. Node.js helped companies like Netflix, Uber, and PayPal move to microservices successfully.

NPM and the Power of Community
Another reason Node.js changed web development is its ecosystem. NPM grew into the largest collection of open-source libraries in the world. Instead of reinventing the wheel, developers could install packages to handle almost any task, from authentication to image processing.

Example of installing a package:
npm install axios

And then using it in your app:
const axios = require('axios');

async function fetchData() {
  const res = await axios.get('https://jsonplaceholder.typicode.com/posts/1');
  console.log(res.data);
}

fetchData();

This speed of development and access to community-driven code drastically reduced the time it takes to build applications.

Performance and Scalability
One of the key reasons big companies adopted Node.js is performance. Its non-blocking I/O and lightweight design make it well-suited for high-traffic applications. For example, Netflix uses Node.js to handle millions of users at the same time while reducing startup time for its applications.

Node.js applications can also scale horizontally by running multiple instances across servers. This flexibility made it one of the most reliable tools for modern web infrastructure.

The Human Side of Node.js
Beyond the technology, Node.js changed how developers work together. Teams no longer need separate specialists for frontend and backend. A single JavaScript team could handle the entire product lifecycle. This made collaboration easier and reduced miscommunication.

It also opened doors for beginners. Learning one language, JavaScript, is enough to start building both client and server code. This lowered the entry barrier for people new to web development.

Conclusion
Node.js did more than just provide a new runtime for JavaScript. It transformed how developers build, scale, and think about web applications. From real-time communication to microservices and from frontend to backend unification, Node.js brought speed, flexibility, and simplicity to the web. The next time you use a streaming platform, ride-sharing app, or live chat feature, there is a good chance Node.js is working behind the scenes. For developers, it continues to be a powerful tool that simplifies complex tasks and makes building modern web applications faster and more enjoyable.