How do you test a NestJS GraphQL resolver with TestingModule?

Q: How do you test a NestJS GraphQL resolver with TestingModule?

describe('UsersResolver', () => { let resolver: UsersResolver; let usersService: jest.Mocked ; beforeEach(async () => { const module = await Test.createTestingModule({ providers: [ UsersResolver, { provide: UsersService, useValue: { findAll: jest.fn(), findOne: jest.fn(), create: jest.fn(), }, }, ], }).compile(); resolver = module.get(UsersResolver); usersService = module.get(UsersService); }); it('findAll returns array of users', async () => { const users = [{ id: 1, email: 'a@test.com' }]; usersService.findAll.mockResolvedValue(users); const result = await resolver.findAll(); expect(result).toEqual(users); expect(usersService.findAll).toHaveBeenCalledTimes(1); }); it('createUser re-throws service errors', async () => { usersService.create.mockRejectedValue(new Error('Email taken')); await expect( resolver.createUser({ email: 'a@test.com', password: 'pass' }) ).rejects.toThrow('Email taken'); }); }); 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.

Difficulty: 5/10

TestingModule, GraphQL resolver, mocking dependencies

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.

Resolver unit test with mocked services

Resolver testing strategy:

1
Unit tests call resolver methods directly — no GraphQLModule, HTTP server, or schema needed.
2

How do you test a NestJS GraphQL resolver with TestingModule?

Difficulty: 5/10

TestingModule, GraphQL resolver, mocking dependencies

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.

Resolver unit test with mocked services

Resolver testing strategy:

1
Unit tests call resolver methods directly — no GraphQLModule, HTTP server, or schema needed.
2

How do you test a NestJS GraphQL resolver with TestingModule?

How do you test a NestJS GraphQL resolver with TestingModule?

Scenario Questions

Follow-up Questions