backend-testing

Testing NestJS APIs on Fastify with Vitest - backend test pyramid, SWC config for decorator metadata, Test.createTestingModule with provider overrides, Fastify inject e2e with a shared configureApp, disposable database strategy with Prisma, test data builders, fakes for clock, ids, mail, queues and HTTP upstreams, OpenAPI contract tests, background job tests, auth, validation and error-shape tests, flaky-test rules, and coverage as a signal. Load when writing or fixing API tests, configuring Vitest, setting up test databases, or deciding what level to test at.