How do you mock a repository in a NestJS unit test?

Q: How do you mock a repository in a NestJS unit test?

// Reusable mock factory export const createMockRepository = (): jest.Mocked > => ({ find: jest.fn(), findOne: jest.fn(), findOneOrFail: jest.fn(), findAndCount: jest.fn(), save: jest.fn(), create: jest.fn(), delete: jest.fn(), update: jest.fn(), increment: jest.fn(), createQueryBuilder: jest.fn().mockReturnValue({ where: jest.fn().mockReturnThis(), andWhere: jest.fn().mockReturnThis(), leftJoinAndSelect: jest.fn().mockReturnThis(), skip: jest.fn().mockReturnThis(), take: jest.fn().mockReturnThis(), getMany: jest.fn(), getOne: jest.fn(), }), } as any); // Test describe('UsersService', () => { let service: UsersService; let userRepo: jest.Mocked >; beforeEach(async () => { const module = await Test.createTestingModule({ providers: [ UsersService, { provide: getRepositoryToken(User), useValue: createMockRepository() }, ], }).compile(); service = module.get(UsersService); userRepo = module.get(getRepositoryToken(User)); }); it('findOne throws NotFoundException for unknown id', async () => { userRepo.findOne.mockResolvedValue(null); await expect(service.findOne(999)).rejects.toThrow(NotFoundException); }); }); getRepositoryToken(Entity) from @nestjs/typeorm is the correct provider token — matches @InjectRepository(). Create a reusable mock factory so every test file gets a fresh mock object. Mock createQueryBuilder() with a chainable object that returns this for builder methods. Use mockResolvedValue() for async repository methods; mockReturnValue() for synchronous ones. Retrieve the mock with module.get(getRepositoryToken(User)) to configure per-test return values.

Difficulty: 5/10

Dependency Injection, Testing, Mocking

Create a mock factory that returns jest.fn() stubs for every Repository method. Provide it using the getRepositoryToken(Entity) token from @nestjs/typeorm — this matches the token used internally by @InjectRepository(). Retrieve the mock after compiling the module with module.get(getRepositoryToken(Entity)).

Repository mock factory and test setup

Repository mocking rules:

1
getRepositoryToken(Entity) from @nestjs/typeorm is the correct provider token — matches @InjectRepository().

How do you mock a repository in a NestJS unit test?

Difficulty: 5/10

Dependency Injection, Testing, Mocking

Create a mock factory that returns jest.fn() stubs for every Repository method. Provide it using the getRepositoryToken(Entity) token from @nestjs/typeorm — this matches the token used internally by @InjectRepository(). Retrieve the mock after compiling the module with module.get(getRepositoryToken(Entity)).

Repository mock factory and test setup

Repository mocking rules:

1
getRepositoryToken(Entity) from @nestjs/typeorm is the correct provider token — matches @InjectRepository().

How do you mock a repository in a NestJS unit test?

How do you mock a repository in a NestJS unit test?

Scenario Questions

Follow-up Questions