Integration Testing

Understand what integration testing covers that unit tests miss, when to write integration tests, and the key differences in test setup, speed, and confidence between the two layers.

Use Supertest to send real HTTP requests to Express applications in tests, assert on status codes, response headers, JSON bodies, and test error handling without starting a real server.

Test database interactions using real PostgreSQL in Docker via Testcontainers, Prisma migrations, transaction rollbacks for fast isolation, and data factories for readable test setup.

Write integration tests that cover the full authentication lifecycle: registration, login, JWT issuance, protected route access, token refresh, and logout with cookie invalidation.

Intercept HTTP calls to third-party APIs in integration tests using Mock Service Worker (MSW) and nock, keeping tests fast and deterministic without real network calls.

Set up NestJS testing modules, override providers with mocks, test controllers and services wired together, and write end-to-end NestJS tests using the full application context.

Verify that API endpoints correctly implement pagination with cursors and offsets, filter data by multiple criteria, sort results, and serialise response payloads without leaking sensitive fields.

Apply proven integration test patterns: fixture loading, factory functions with builder pattern, shared database helpers, and the object-mother pattern for managing complex test data setup.

Keep integration test suites fast, reliable, and maintainable by applying proven isolation strategies, detecting and eliminating flaky tests, and establishing team conventions for sustainable growth.

Configure GitHub Actions to run integration tests with PostgreSQL service containers, run migrations automatically, publish test results, and gate pull request merges on passing integration tests.