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
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.
