nest-service-test

Writes the service layer tests of a use case (UC-XXX) in a NestJS application with Vitest: every business rule with its allowed and its rejected case, every alternative flow the service decides, and the main success scenario, called on the real service against a real PostgreSQL database in Testcontainers, nothing mocked in the call chain. Checks the Vitest transformer that decorator metadata needs, and owns the shared test setup and the per-use-case seed test/data/uc<id>-<slug>.ts. Files are test/UC-XXX-<slug>.service-spec.ts. Use when the user asks to "test the service layer", "test the business rules", "write service tests", or mentions NestJS testing, Vitest, Testcontainers, domain errors, or business rule tests for a NestJS use case. Run by /use-case-test as the integration layer of a use case offered through the service alone, or when the service layer is named; below a REST entry layer the API tests cover the service. Can also be run directly.