Test Strategy

Testing Pyramid

Balance between different test types.

The Pyramid

        /
       / E2E (10%) \
      /  Slow, Expensive  \
     /--------------------\
    / Integration (20%)     \
   /   Moderate Speed/Cost    \
  /--------------------------\
 / Unit Tests (70%)            \
/  Fast, Cheap, Many            \
/--------------------------------\

Test Distribution

Type	%	Speed	Cost	Confidence
Unit	70%	Fast	Low	Low
Integration	20%	Medium	Medium	Medium
E2E	10%	Slow	High	High

Anti-Patterns

1. Ice Cream Cone: More E2E than unit tests
2. Funnel: All tests are E2E
3. Hourglass: No integration tests

When to Use Each

Unit Tests:

• Pure functions
• Utility functions
• Complex logic
• Business rules

Integration Tests:

• Component interactions
• API integrations
• State management
• Form submissions

E2E Tests:

• Critical user journeys
• Checkout flows
• Authentication
• Cross-browser testing

What to Test First

Prioritize tests based on value.

Priority Matrix

1. Critical business logic (highest priority)

   • Payment processing
   • Authentication
   • Data validation

2. Complex components

   • Forms with validation
   • Interactive widgets
   • Data displays

3. Edge cases

   • Error handling
   • Empty states
   • Loading states

4. UI details (lowest priority)

   • Styling
   • Animations
   • Responsive design

Testing Checklist

## Must Test
- [ ] Authentication flows
- [ ] Payment processing
- [ ] Form validation
- [ ] Error handling
- [ ] Data CRUD operations

## Should Test
- [ ] Complex business logic
- [ ] Component interactions
- [ ] API integrations
- [ ] State management

## Nice to Test
- [ ] UI edge cases
- [ ] Responsive behavior
- [ ] Accessibility

TDD vs BDD

TDD (Test-Driven Development)

1. Red: Write failing test
2. Green: Write minimal code to pass
3. Refactor: Improve code quality

// TDD Example
// 1. Write test first
it('should calculate total price', () => {
  expect(calculateTotal([10, 20, 30])).toBe(60);
});

// 2. Write implementation
function calculateTotal(prices) {
  return prices.reduce((sum, price) => sum + price, 0);
}

BDD (Behavior-Driven Development)

Given - Context
When - Action
Then - Expected outcome

// BDD Example
describe('Shopping Cart', () => {
  it('should calculate total when items are added', () => {
    // Given
    const cart = new ShoppingCart();
    
    // When
    cart.addItem({ price: 10 });
    cart.addItem({ price: 20 });
    
    // Then
    expect(cart.total).toBe(30);
  });
});

Comparison

Aspect	TDD	BDD
Focus	Code behavior	Business behavior
Language	Technical	Domain-specific
Collaboration	Developers	Everyone
Documentation	Code	Living docs

When to Use

Use TDD when:

• Building complex algorithms
• Working on infrastructure
• Need precise code coverage

Use BDD when:

• Cross-functional teams
• Complex business rules
• Need shared understanding

Tools

• TDD: Jest, Vitest, Mocha
• BDD: Cucumber, Jest with describe/it