---

name: strategy description: Testing philosophy, patterns, and quality metrics. Covers the testing pyramid, test design patterns (AAA, BDD, fixtures, factories), edge case checklists, and debugging flaky tests.

Testing Strategy

Core testing philosophy and patterns for building reliable, maintainable test suites.

The Testing Pyramid

Copy        /\
       /  \
      / E2E \       Few, slow, high-confidence
     /--------\
    /Integration\   Some, medium speed
   /--------------\
  /     Unit       \  Many, fast, focused
 /------------------\

Good Tests Are (FIRST)

Quality Metrics

Test Design Patterns

Arrange-Act-Assert (AAA)

Copyit('should calculate total with tax', () => {
  // Arrange
  const items = [{ price: 10, quantity: 2 }];
  const taxRate = 0.08;
  
  // Act
  const total = calculateTotal(items, taxRate);
  
  // Assert
  expect(total).toBe(21.6);
});

Given-When-Then (BDD)

Copydescribe('User login', () => {
  describe('given valid credentials', () => {
    describe('when user submits login form', () => {
      it('then they should be redirected to dashboard', async () => {
        // Test implementation
      });
    });
  });
});

Test Fixtures

Copy// fixtures/users.ts
export const validUser = {
  email: 'test@example.com',
  password: 'SecurePass123!',
  name: 'Test User'
};

export const adminUser = {
  ...validUser,
  email: 'admin@example.com',
  role: 'admin'
};

Factory Pattern

Copy// factories/user.ts
export function createUser(overrides = {}) {
  return {
    id: faker.datatype.uuid(),
    email: faker.internet.email(),
    name: faker.name.fullName(),
    createdAt: new Date(),
    ...overrides
  };
}

// In tests
const user = createUser({ role: 'admin' });

Edge Cases Checklist

Input Validation

• Empty string / null / undefined
• Whitespace-only strings
• Maximum length inputs
• Special characters / Unicode / emoji
• Negative numbers / Zero / Very large numbers
• Invalid date formats

Collections

• Empty array/object
• Single item
• Many items (performance)
• Duplicate items
• Unsorted input

Async Operations

• Success case
• Timeout
• Network error
• Partial failure
• Retry behavior

Authentication/Authorization

• Unauthenticated access
• Invalid/expired token
• Insufficient permissions
• Cross-user data access

Debugging Flaky Tests

Common Causes & Fixes

Isolation Fix

Copy// Bad: Shared state
let counter = 0;
it('test 1', () => { counter++; });
it('test 2', () => { expect(counter).toBe(0); }); // Fails!

// Good: Reset in beforeEach
let counter: number;
beforeEach(() => { counter = 0; });

Test Types Summary

Tools by Type