Test-driven development (TDD)

What is test-driven development?

Test-driven development is a practice where you write the test before the code it checks. The rhythm has a name, red-green-refactor, and it repeats. Write a test for the behaviour you want. It fails, because the code doesn't exist yet. Write the minimum code to make it pass. Then clean up the structure without breaking the test. Round again.

Writing the test first forces you to decide what a piece of code should do before deciding how it'll do it. That sounds like a small reordering, but it changes the design. Take a function that calculates shipping cost: the test states the inputs and the expected total before a single line of logic exists, so the requirement is pinned down first and the implementation has a clear target to hit. Every piece of logic arrives with a test already wrapped around it.

TDD takes discipline, and it's slower in the first hour and faster across the project. Code written this way tends to be more modular, documented by its own tests, and safe to refactor later because the suite tells you the instant something breaks. It's a development practice, not a testing afterthought, which is the whole reason it works.

TDD at Dallonses

We reach for TDD on the parts of a system where correctness isn't negotiable: payment logic, pricing rules, anything where a silent bug costs real money. Writing the test first keeps us honest about the requirement, and it leaves behind a suite that documents intent better than a comment ever could.

It isn't dogma. We don't test-drive a throwaway prototype, and we'll say so. Where TDD earns its cost, the tests fold straight into our automated testing and CI pipeline, so the same checks that shaped the code keep guarding it on every release. Our software quality assurance work is stronger for it, and so is the client's confidence in changing the code months from now.

Building logic that has to be right the first time? Let's test-drive the parts that matter.

Talk to us about QA