TDD

Test-Driven Development

Write the failing test first, then the code that makes it pass.

When you'd see it: Software development practice discussions. TDD means writing the test before the code.

Why it matters: In TDD you write a failing test first, then the code to pass it, which forces clear requirements and leaves a safety net of tests. It slows the first write and speeds every change after.

Common mistakes: Writing tests after the code and calling it TDD. The discipline is test-first, which is what shapes the design.