What is Test-Driven Development? - Explanation & Meaning

Definition

Test-driven development (TDD) is a software development method where you first write a failing test, then write the minimal code to make the test pass, and finally refactor the code. This cycle, known as red-green-refactor, leads to better designed, more reliable software.

Technical explanation

The TDD cycle consists of three steps: Red (write a test that fails because the functionality does not exist yet), Green (write the minimal code to make the test pass, without worrying about elegance), and Refactor (improve the code while the test stays green). The testing pyramid defines the ideal ratio: many unit tests at the base, fewer integration tests in the middle, and few end-to-end tests at the top. TDD forces developers to think about desired behavior before writing the implementation, leading to better API designs and looser coupling. Behavior-Driven Development (BDD) extends TDD with a focus on business behavior, described in Given-When-Then format. TDD works best for business logic, algorithms, and pure functions. It is less suitable for UI components, external integrations, and exploratory code. Benefits include higher test coverage, faster feedback, fewer regression bugs, and code that is inherently designed to be testable.

How MG Software applies this

MG Software applies TDD for complex business logic and API endpoints where reliability is crucial. We write tests-first for data processing logic, authorization rules, and financial calculations. For UI components, we use a pragmatic approach where we write tests alongside the implementation. Our CI/CD pipeline blocks merges when tests fail, maintaining TDD discipline.

Practical examples

• A developer writing a test first for a discount calculation function, then building the implementation, discovering that the original specification missed an edge case for combined discounts.
• A team applying TDD for an API endpoint and designing a more intuitive API interface as a result because they start from the user perspective (the test).
• A financial system where TDD guarantees every calculation is correct by covering hundreds of test cases before the code goes to production.

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