until-destroy: Calling ngOnDestroy on test does not complete subscription

"@angular/core": "9.0.2",
"rxjs": "6.5.4",
"@ngneat/until-destroy": "7.1.1",
"jasmine-core": "3.5.0",

On a component defined as

@UntilDestroy()
@Component({
  templateUrl: 'none-improvement.html',
  selector: 'cv-none-improvement-page',
  styleUrls: ['none-improvement.scss']
})
export class NoneImprovementPageComponent implements OnInit, OnDestroy {
  public firstName: string;

  constructor(
    private _user: UserProfileStore,
  ) {
  }

  public ngOnInit() {
    this._user.profile$
      .pipe(
        untilDestroyed(this)
      )
      .subscribe(u => this.firstName = u.get('firstName'));
  }

  public ngOnDestroy() {
    //
  }
}

I write this test:

  it('stops getting first name from user profile after destroy', () => {
    expect(sut.firstName).toBeUndefined();
    sut.ngOnInit();
    mockUserProfileStore.profileSubject$.next(new UserProfile(<any>{ firstName: 'testName' }).toImmutable());
    expect(sut.firstName).toEqual('testName');
    sut.ngOnDestroy();
    mockUserProfileStore.profileSubject$.next(new UserProfile(<any>{ firstName: 'newName' }).toImmutable());
    expect(sut.firstName).toEqual('testName');
  });

which fails. But if I use untilDestroyed(this, 'ngOnDestroy') passes. Is ngOnDestroy not the default method that triggers the unsubscription?