How do you unit-test a module that uses a dynamic module dependency in NestJS?

Q: How do you unit-test a module that uses a dynamic module dependency in NestJS?

describe('UsersService', () => { let service: UsersService; beforeEach(async () => { const module = await Test.createTestingModule({ providers: [ UsersService, // Replace what DatabaseModule.forRoot() would have provided { provide: DB_OPTIONS, useValue: { url: 'sqlite:///:memory:' }, }, { provide: DatabaseService, useValue: { query: jest.fn().mockResolvedValue([]), save: jest.fn(), }, }, ], }).compile(); service = module.get(UsersService); }); it('finds users', async () => { const result = await service.findAll(); expect(result).toEqual([]); }); }); Provide mock values for the tokens the dynamic module registers, not the module itself. This isolates the test from infrastructure — no real database, HTTP client, or external service needed. Use overrideProvider() when importing the real module graph but needing to swap one provider. Export all token constants from your dynamic modules so tests can reference them without magic strings.

Difficulty: 5/10

Dynamic Modules, TestingModule, Provider Override

Use Test.createTestingModule() and provide mock values for the tokens that the dynamic module would have registered. This avoids spinning up the real dynamic module — which might connect to a real database — while still testing the service logic correctly.

Unit testing a service that depends on a dynamic module token

Testing strategy for dynamic module dependencies:

1
Provide mock values for the tokens the dynamic module registers, not the module itself.
2
This isolates the test from infrastructure — no real database, HTTP client, or external service needed.
3

How do you unit-test a module that uses a dynamic module dependency in NestJS?

Use Test.createTestingModule() and provide mock values for the tokens that the dynamic module would have registered. This avoids spinning up the real dynamic module — which might connect to a real database — while still testing the service logic correctly.

Scenario Questions

Follow-up Questions