How do you mock services in Angular tests?

Short answer: Provide a mock implementation of the service in TestBed using the providers array. Use useClass, useValue, or useFactory to inject mocks.

Example code

class MockDataService { getData() { return of(['mock data']); } } beforeEach(() => { TestBed.configureTestingModule({ providers: [{ provide: DataService, useClass: MockDataService }] }); });

Real-world example (ShopNest)

A shared CartService is injected into header and product pages so both see the same cart count.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.