testing

Skill: testing

Testing

Overview

Testing strategy across unit, component, integration, and end-to-end testing suites using Vitest, React Testing Library, and Playwright.

When to Use

Activate for any task involving unit tests, integration tests, E2E testing, TDD/BDD workflows, or fixing regression bugs.

Rules & Patterns

️ The ContextOS Testing Pyramid

      /\
     /E2E\       10% — Playwright (Critical user journeys, auth, checkout)
    /-----\
   / Integ \     20% — API & Component Integration (RTL + MSW / Supertest)
  /---------\
 /   Unit    \   70% — Pure functions, Domain Entities, Utils (Vitest)
/-------------\

Negative Constraints (What NOT to Do)

1. NEVER mock internal implementation details: Mock ONLY external I/O boundaries (HTTP network requests via MSW, Database via test containers or in-memory DB).
2. NEVER test implementation details: In React Testing Library, query by user-facing roles (getByRole, getByLabelText), NEVER by CSS selectors or internal component state.
3. NEVER write assertions without an expected failure mode: Each test must test a single logical behavior and fail if that behavior breaks.
4. NEVER leave flaky tests or arbitrary sleep (await delay(1000)): Always use waitFor() or explicit event triggers with timeouts.
5. NEVER share mutable state between tests: Every test must have isolated state via beforeEach() setup and clean reset.

AAA Standard Pattern

describe('Feature / Unit', () => {
  it('should achieve expected outcome when given specific condition', async () => {
    // 1. ARRANGE
    const user = createTestUser({ role: 'admin' });
    // 2. ACT
    const result = await processOrder(user, sampleCart);
    // 3. ASSERT
    expect(result.status).toBe('confirmed');
  });
});

Code Examples

See EXAMPLES.md for detailed anti-patterns and production testing code.

Validation Checklist

• Tests follow Arrange-Act-Assert (AAA) structure
• No brittle CSS selectors or private state inspections
• Mocks isolated strictly to network/IO boundaries (MSW)
• Fast execution (< 5s for unit suite) with zero flaky sleeps