feat: add testing-patterns skill

[4444J99]

Summary

Adds a comprehensive testing-patterns skill covering the full testing stack:

• Testing philosophy — Testing Trophy model, what to test vs. what NOT to test
• Unit testing — AAA pattern, test naming, pure functions, edge cases
• React component testing — Testing Library, query priority, async testing, mocking
• Integration testing — API route testing, database integration
• E2E testing — Playwright setup, Page Object Pattern, visual regression
• Mocking strategies — When to mock, MSW (Mock Service Worker)
• Test configuration — Vitest config, test setup
• Coverage strategy — Meaningful coverage targets, CI integration

Motivation

Testing is one of the most frequently requested development topics. This skill complements the existing webapp-testing skill (which focuses on browser automation) by covering the broader testing landscape from unit tests to CI integration.

Format

Follows the standard skill format: SKILL.md with name and description frontmatter, self-contained in skills/testing-patterns/.

[4444J99]

Checking in — happy to address any feedback or adjust the skill structure. The testing-patterns skill draws from the Testing Trophy model and covers unit, integration, E2E, and visual regression patterns. Let me know if anything needs revision.

[4444J99]

All checks passing — ready for review when you get a chance.