What is TDD?

Brief Answer

• TDD (Test‑Driven Development) — write a test first, then minimal code to pass it, then refactor.
• Cycle: Red → Green → Refactor.
• Benefits: better design, fewer regressions, confidence in changes.

Full Answer

What TDD is

TDD is an iterative process: define behavior via a failing test (Red), add minimal code to pass (Green), then improve the design without changing behavior (Refactor).

TDD cycle

1. Red: write a test that fails.
2. Green: write the smallest code to pass.
3. Refactor: improve structure while tests stay green.

Mini example:

// Red: failing test — function missing or behavior not implemented
expect(sum(1, 2)).toBe(3);
 
// Green: minimal implementation
function sum(a, b) { return a + b; }

Advantages

• Behavior‑driven API design.
• Fast feedback and regression safety.
• Confidence during refactors and feature work.

Common mistakes

• Writing overly generic tests — losing focus.
• Skipping refactor — technical debt grows.
• Taking huge steps — losing red/green rhythm.

Tips

• Small steps, simplest code at Green.
• Refactor immediately, guided by tests.
• Keep tests fast and deterministic.