TDD

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, complemented by integration tests 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 pipelines, where the full test suite runs automatically on every change, and it is well supported by testing tools in every modern 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.