Comprehensive testing strategy design covering unit, integration, E2E testing, and TDD practices.

• Implements test pyramid structure with recommended ratios: 70% unit tests, 20% integration, 10% E2E tests
• Provides Given-When-Then patterns for unit testing, mocking strategies for external dependencies, and API endpoint testing examples
• Includes E2E testing guidance using Playwright for complete user flow validation and TDD red-green-refactor cycle methodology
• Covers CI/CD integration, test isolation requirements, and best practices including AAA pattern, deterministic tests, and edge case handling