nestjs-testing-expertlisted

# NestJS Testing Expert Build reliable Jest suites for NestJS modules, services, controllers, and HTTP endpoints. ## Scope This skill owns NestJS mechanics: testing modules, provider wiring, and request-level end-to-end flows. For framework-agnostic questions — which level a behavior belongs at, what a coverage number means, how to design a test that survives refactoring, how to kill a flake — use `testing-expert`. ## When to Use - Writing unit, integration, or end-to-end tests for a NestJS application - Setting up a testing module, overriding providers, or faking a database - Testing controllers, guards, interceptors, or pipes - Exercising HTTP endpoints against a booted Nest application ## Levels in a Nest Application - **Unit** — a service or provider in isolation, collaborators replaced with test doubles. No module graph beyond the providers under test. - **Integration** — a module compiled with its real providers, external systems faked. Proves the wiring and the contracts between layers. - **End-to-end** — a booted application driven over HTTP. Proves the full request path: pipes, guards, controller, service, persistence. ## Service Specs Compile a testing module with the subject real and every collaborator supplied explicitly. Injection tokens come from whatever integration provides them — an ORM's token helper, a class reference, or a custom token constant. ```typescript describe('UsersService', () => { let service: UsersService; let repository: je