Testing Skills

Skills for AI coding agents with best testing practices based on amazing articles by Artem Zakharchenko on EpicWeb. Source articles available in the src/ folder.

Installation

Install with npm:

npx skills add MonsterDeveloper/testing-skills --skill testing-best-practices

or bun:

bunx skills add MonsterDeveloper/testing-skills --skill testing-best-practices

Skill Structure

testing-best-practices/
├── SKILL.md                            # Core principles and patterns
└── references/
    ├── vitest-patterns.md              # Vitest config, async, mocks
    └── component-testing.md            # Component/UI test patterns

The skill is designed for context window efficiency:

• SKILL.md (~200 lines) contains essential principles loaded when the skill triggers
• Reference files are loaded only when needed for detailed patterns

Key Principles

1. Test intentions, not implementations — Tests should fail only when user-facing behavior breaks
2. The Golden Rule of Assertions — A test must fail if, and only if, the intention behind the system is not met
3. Don't assert on requests — Validate in mocks, assert on UI state
4. Use real browsers — JSDOM creates false confidence; prefer Vitest Browser Mode
5. Flat, explicit tests — Avoid nested describe and scattered hooks
6. Code coverage is a tool, not a target — Never let it drive testing decisions

Topics Covered

• Test structure (Setup → Action → Assertion)
• Test boundaries and mocking principles
• Assertion patterns (.resolves, .toBeVisible, inverse assertions)
• Mock management (.mockClear() vs .mockReset() vs .mockRestore())
• S.M.A.R.T. framework for flaky tests
• Vitest Browser Mode setup and patterns
• Component testing with MSW
• Disposable objects for test cleanup

Source Articles

Based on 18 articles from EpicWeb covering:

• The True Purpose of Testing
• The Golden Rule of Assertions
• Anatomy of a Test
• Test Boundaries
• Implicit Assertions
• Inverse Assertions
• Vitest Defaults and Browser Mode
• Why Not JSDOM
• And more...