Introduction to TDD with Node.js

Overview

This course is about building a backend service from behavior, not implementation.

We will use Test-Driven Development (TDD) — writing a failing test before any production code — to build a URL shortener API with TypeScript, Fastify, PostgreSQL, Jest, and Docker.

By the end, you'll be able to take a feature from a failing test all the way to production-ready code, without losing control as the system grows.

Why TDD with Node.js

Early in my career, I kept hearing that tests mattered. But on real projects, they were usually the first thing cut once deadlines got tight. That gap — between what teams say and what they do — is a big reason I made this course.

Node.js is a great place to learn TDD because the feedback loop is short:

• Write a test
• Run it in seconds
• See whether the behavior is correct

That makes the Red → Green → Refactor cycle something you feel, not just understand.

The course stays practical. We build one service from start to finish, keep the scope clear, and add real problems only when we actually need them.

A quick note: TDD does feel slower at first, and you'll sometimes wonder whether the test-first step is worth it. That's normal. The goal here is to shorten that awkward phase through repeated practice on a single project.

Who This Course Is For

This course is for engineers who know backend basics and want a better testing workflow.

You don't need prior Fastify or PostgreSQL experience, but you should already be comfortable with:

• Node.js fundamentals
• JavaScript or TypeScript, including async / await
• REST API basics
• SQL and relational database basics
• Git commands like clone, checkout, and commit

If you're brand new to Node.js, this will move too fast. But if you can already read backend code and want a more disciplined way to write it, you're in the right place.

How to Use the Repository

All source code lives on GitHub:

👉 test-driven-development-tdd-with-nodejs-course

Most hands-on chapters have two branches:

Workflow: start from the start branch, write the code yourself, and use the finish branch only to compare or recover if you get stuck.

A few notes on numbering:

• This introduction has no coding branch.
• The first branch appears in the next chapter as 01-what-is-tdd-start.
• That numbering is intentional — branch numbers track the hands-on chapters, not the markdown file numbers.
• The main branch holds the final version of the project.

What We Will Build

We're building a URL shortener API — a service that:

1. Accepts a long URL
2. Returns a short code
3. Later redirects users to the original address

The idea is simple, which is exactly what makes it a good TDD project. The behavior is easy to describe, but the implementation still leaves room to practice real backend work:

• Request and response design
• Route testing
• Application structure
• Database integration
• Input validation
• Concurrency and collision handling
• Test isolation and CI

We'll start with a tiny example in plain Node.js so the TDD loop is easy to see. Then we move into the real project: a Fastify API in TypeScript, backed by PostgreSQL, built step by step as the system grows.

The progression is deliberate:

1. Learn the Red-Green-Refactor cycle with a small Node.js example.
2. Set up the Fastify project and write the first failing integration-style test.
3. Implement URL shortening with the smallest possible code, then replace the fake with real logic.
4. Move from in-memory storage to PostgreSQL without breaking existing behavior.
5. Expand the API with redirects, click tracking, listing, stats, and deletion.
6. Harden the service with validation, collision handling, better test infrastructure, and CI.

The project stays understandable from start to finish. We add complexity in layers, and the test suite tells us whether each step was safe.

What to Expect

This is not a course where we write code first and bolt tests on later. The test comes first whenever the behavior is clear enough to describe.

Expect to see:

• Failing output, often
• Small steps
• Code that is simple before it becomes elegant

That's not a flaw in the process — that is the process.

In production, this gives you more than coverage. It gives you fast feedback: when a change breaks behavior, you know quickly; when a refactor is safe, you know quickly.

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Next up: we'll make TDD concrete with a tiny Node.js example before moving into the Fastify application.