# Testing Mastery

> Unified testing skill — TDD workflow, unit/integration patterns, E2E/Playwright strategies. Replaces tdd-workflow + testing-patterns + webapp-testing. Use when this capability is needed.

- Skill: `tomevault-io/testing-mastery` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add tomevault-io/testing-mastery`
- Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/testing-mastery/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs
- Author: tomevault-io (https://skillmd.com/u/tomevault-io)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/tomevault-io/testing-mastery

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# 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](references/tdd-cycle.md) |
| Write unit/integration tests | Mocking, data strategies, patterns | [unit-integration.md](references/unit-integration.md) |
| Test critical user flows in browser | E2E with Playwright | [e2e-playwright.md](references/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.

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<!-- tomevault:4.0:skill_md:2026-04-16 -->