Testing en Node.js con Vitest 4/5, node:test, Playwright y MSW. Cubre unit tests, integration tests, mocking (vi.fn, MSW), Testcontainers, snapshot testing, coverage, y TDD. Stack recomendado 2026: Vitest + Playwright + MSW + Testcontainers. Actívala al escribir tests, configurar CI/CD, o definir estrategia de testing.
