Test-Driven Development (TDD) Explained

What is TDD?

Test-Driven Development is a practice where you write tests before writing the code. It leads to better design and reliable, well-tested code.

The Red-Green-Refactor Cycle

1. Red — write a failing test.
2. Green — write minimal code to pass it.
3. Refactor — clean up while keeping tests green.

TDD in Action

// 1. RED — write the test first
test("reverses a string", () => {
  expect(reverse("abc")).toBe("cba");
});
// Fails — reverse doesn't exist yet

// 2. GREEN — make it pass
function reverse(str) {
  return str.split("").reverse().join("");
}

// 3. REFACTOR — improve if needed, tests stay green

Benefits

• Forces clear requirements upfront.
• High test coverage by default.
• Confidence to refactor.
• Better, more modular design.

Drawbacks

• Slower initial development.
• Learning curve.

FAQs

Is TDD always worth it?

Great for complex logic; may be overkill for simple UI tweaks. More in our Testing guides.

TDD vs BDD?

BDD (Behavior-Driven) focuses on user behavior in plain language; TDD on code units.