---
title: "TDD"
description: "TDD is a development practice where you write a failing test before the code that makes it pass. See how the red-green-refactor cycle shapes better code."
url: "https://nodea.io/en/glossary/tdd"
lang: "en"
updated: "2026-07-13"
---

# TDD

> TDD (Test-Driven Development) is a practice in which a developer writes a failing test first, then the minimal code to pass it, and finally refactors.

**TDD** (Test-Driven Development) is a software development practice in which you write an automated test *before* writing the code that is supposed to satisfy it. The test initially fails, then you write just enough code to make it pass, and finally you clean up the design. This inverts the usual order, where tests — if written at all — come after the implementation.

## The red-green-refactor cycle

TDD follows a short, repeating loop. First, red: you write a small test describing a desired behaviour, and it fails because the feature does not exist yet. Second, green: you write the minimal code needed to make the test pass. Third, refactor: with the test guarding correctness, you improve the structure of the code without changing its behaviour. The cycle repeats in tiny increments, keeping the codebase covered by tests at every step.

## Why teams use TDD

The tests written during TDD are usually [unit tests](https://nodea.io/en/glossary/unit-testing), complemented by [integration tests](https://nodea.io/en/glossary/integration-testing) at a higher level. Writing them first tends to produce simpler, more modular designs, because code that is hard to test is often code that is hard to use. The accumulated tests form a safety net that catches regressions immediately and gives developers confidence to change code later. TDD fits naturally into [CI/CD](https://nodea.io/en/glossary/ci-cd) pipelines, where the full test suite runs automatically on every change, and it is well supported by testing tools in every modern [framework](https://nodea.io/en/glossary/framework). While TDD demands discipline and upfront effort, teams that adopt it consistently often report fewer defects and more maintainable code over the life of a project.

### Does TDD slow development down?

It adds effort up front but usually saves time overall. Writing tests first catches defects early, encourages simpler designs and produces a safety net that makes later changes far less risky than in untested code.

## Related

- [Unit testing](https://nodea.io/en/glossary/unit-testing)
- [CI/CD](https://nodea.io/en/glossary/ci-cd)
- [Framework](https://nodea.io/en/glossary/framework)
- [Integration testing](https://nodea.io/en/glossary/integration-testing)

---

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