example.spec.ts

@Injectable({
  providedIn: 'root',
})
export class SomeService {
  doSomething() {
    console.log('test');
  }
}

@Component({
  selector: 'some-component',
  template: '',
})
export class SomeComponent implements OnInit {
  constructor(private service: SomeService) {}
  ngOnInit(): void {
    this.service.doSomething();
  }
}

describe('SomeComponent', () => {
  let service: SomeService;
  let component: SomeComponent;
  let fixture: MockedComponentFixture<SomeComponent>;

  beforeEach(() => {
    // In this example i'm using 'keep' because in real situation i can not mock dependency,
    // but want to spy on it methods
    return MockBuilder(SomeComponent).keep(SomeService);
  });

  beforeEach(() => {
    service = TestBed.inject(SomeService);
    spyOn(service, 'doSomething');

    fixture = MockRender(SomeComponent);
    component = fixture.point.componentInstance;
  });

  it('should do something initially', () => {
    expect(service.doSomething).toHaveBeenCalled();
  });
});