Test-Driven Development

Test-driven development is a software engineering method in which a programmer writes an automated test for a small piece of intended functionality before writing the code that implements it, then writes just enough code to make that test pass, and finally refactors the code to improve its structure while keeping the test passing, repeating this cycle for each new piece of functionality. The practice, popularized by Kent Beck as part of extreme programming in the late 1990s, aims to produce a comprehensive suite of automated tests as a natural byproduct of writing the code itself, catching regressions early and giving developers confidence to change or refactor a codebase without breaking existing behavior.