How to test relative router.navigate?

Question

Angular

there is this piece of code:

navigateTo() {
   this.router.navigate(['.', 'testUrl'], {
      relativeTo: this.activatedRoute,
    });
}

I test like this:

beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [
        RouterTestingModule.withRoutes([
          {
            path: 'testUrl',
            component: TestComponent
          },
        ]),
      ]
      })
     })

     it('', async( async () => {
        navigateTo();
        await fixture.whenStable();
        expect(location.path())
         .toBe('/testUrl');
    }))

The fact is that if I rewrite it like this:
this.router.navigate(['.', 'testUrl']);
Then my test will still pass. How to write a test that could be sure that it moved up one level (relatively) and went into urd