testing-tdd-workflow

When to Use

Apply when implementing new features, fixing bugs, or refactoring code. TDD ensures tests drive design and all code is covered.

Patterns

Pattern 1: Red-Green-Refactor Cycle

RED:     Write failing test (test what, not how)
GREEN:   Write minimal code to pass
REFACTOR: Improve code, keep tests green
REPEAT:  Next behavior

Source: https://martinfowler.com/bliki/TestDrivenDevelopment.html

Pattern 2: Test Structure (AAA)

// Source: https://martinfowler.com/bliki/GivenWhenThen.html
it('should calculate total with discount', () => {
  // Arrange (Given)
  const cart = new Cart();
  cart.add({ price: 100, quantity: 2 });

  // Act (When)
  const total = cart.calculateTotal(0.1); // 10% discount

  // Assert (Then)
  expect(total).toBe(180);
});

Pattern 3: One Assertion Per Test

// Source: https://blog.cleancoder.com/uncle-bob/2014/12/17/TheCyclesOfTDD.html
// GOOD: Single behavior per test
it('should add item to cart', () => {
  cart.add(item);
  expect(cart.items).toContain(item);
});

it('should update cart count', () => {
  cart.add(item);
  expect(cart.count).toBe(1);
});

// BAD: Multiple behaviors
it('should add item and update count', () => { /* multiple asserts */ });

Pattern 4: Test Naming Convention

// Format: should [expected behavior] when [condition]
describe('Cart', () => {
  it('should return 0 when cart is empty', () => {});
  it('should apply discount when code is valid', () => {});
  it('should throw error when quantity is negative', () => {});
});

Pattern 5: Outside-In TDD

1. Start with acceptance test (user story)
2. Discover collaborators through failing test
3. Write unit tests for collaborators
4. Implement from inside out
5. Acceptance test passes

Source: https://martinfowler.com/bliki/TestDrivenDevelopment.html

Anti-Patterns

• Test after code - Loses design benefits; tests become afterthought
• Testing implementation - Test behavior, not internal methods
• Large test steps - Keep RED-GREEN cycles small (minutes, not hours)
• Skipping refactor - Technical debt accumulates; refactor is mandatory

Verification Checklist

• Test written BEFORE implementation
• Test fails for the right reason (RED)
• Minimal code written to pass (GREEN)
• Code refactored, tests still pass
• Each test covers one behavior
• Test names describe expected behavior