Create a TestingModule with the resolver class and mocked service providers. Call resolver methods directly — no HTTP server or GraphQLModule required for unit tests. For integration tests that exercise the full GraphQL pipeline, use supertest with the started NestJS application and send raw GraphQL query strings.
Unit tests call resolver methods directly — no GraphQLModule, HTTP server, or schema needed.
Mock services with useValue and jest.fn() — test resolver logic in isolation.
Field resolver tests should pass a mock @Parent() object directly to the method.
Integration tests use supertest to POST a GraphQL query string to the running app.
For subscriptions test the PubSub logic in the service layer — subscription transport is harder to unit test.