Agent Skills: testing-strategy

Load PROACTIVELY when task involves writing tests, improving coverage, or test infrastructure. Use when user says \"add tests\", \"write unit tests\", \"set up E2E testing\", \"improve coverage\", or \"add mocks\". Covers Vitest/Jest unit tests, React Testing Library component tests, Playwright E2E tests, MSW API mocking, test organization and naming, fixture management, coverage targets and thresholds, snapshot testing, and CI integration.