Integration Testing

This walks you through building proper integration tests that actually verify your components work together, not just in isolation. You'll test API endpoints against real databases, validate service-to-service communication, and check authentication flows without mocking away the interesting parts. The guides cover API testing with supertest, database integration with test containers, external service mocking strategies, and message queue validation. The best practices section is practical: use real databases (containerized or in-memory), clean up between tests, and actually test error cases. If you're tired of unit tests passing but production still breaking, this gives you the patterns to catch integration issues before deployment.