tai-ch0802/testing-mastery

Testing Mastery — Unified Testing Skill

Write tests that document intent, catch regressions, and run fast. Choose the right strategy for the right situation.

Decision Tree: Which Testing Strategy?

Is this a new feature?
├─ YES → Use TDD (see references/tdd-cycle.md)
│        Write failing test → Minimal code → Refactor
└─ NO
   ├─ Is this a bug fix?
   │  └─ YES → Write regression test first, then fix
   ├─ Is this a critical user flow (login, checkout)?
   │  └─ YES → E2E test (see references/e2e-playwright.md)
   └─ Is this business logic / data transformation?
      └─ YES → Unit + Integration tests (see references/unit-integration.md)

Testing Pyramid

        /\          E2E (Few, ~10%)
       /  \         Critical user flows only
      /----\
     /      \       Integration (Some, ~20%)
    /--------\      API, DB, service contracts
   /          \
  /------------\    Unit (Many, ~70%)
                    Functions, classes, utilities

Core Principles

| Principle | Rule | |-----------|------| | AAA | Arrange → Act → Assert | | Fast | Unit < 100ms, Integration < 1s | | Isolated | No test depends on another | | Behavior | Test WHAT, not HOW | | Minimal | One assertion per test (ideally) |

Quick Reference

| I need to... | Use | Reference | |--------------|-----|-----------| | Build feature test-first | TDD (RED-GREEN-REFACTOR) | tdd-cycle.md | | Write unit/integration tests | Mocking, data strategies, patterns | unit-integration.md | | Test critical user flows in browser | E2E with Playwright | e2e-playwright.md |

Anti-Patterns (Universal)

| ❌ Don't | ✅ Do | |----------|-------| | Test implementation details | Test observable behavior | | Write tests after shipping | Write tests before/during | | Duplicate test code | Use factories & fixtures | | Complex test setup | Simplify or split | | Ignore flaky tests | Fix root cause | | Skip cleanup | Reset state in teardown | | Multiple asserts per test | One behavior per test |

🔧 Runtime Scripts

| Script | Purpose | Command | |--------|---------|---------| | scripts/test_runner.py | Unified test execution | python scripts/test_runner.py <project_path> | | scripts/playwright_runner.py | Browser E2E testing | python scripts/playwright_runner.py <url> | | | With screenshot | python scripts/playwright_runner.py <url> --screenshot | | | Accessibility check | python scripts/playwright_runner.py <url> --a11y |

Remember: The test is the specification. If you can't write a test for it, you don't understand the requirement.