How to use the @nebular/theme/components/cdk/overlay/overlay-position.NbPosition.START function in @nebular/theme

it('should create strategy with position start and adjustment noop', () => {
    const withPositionsSpy = spyOn(strategy, 'withPositions').and.callThrough();

    strategy.position(NbPosition.START).adjustment(NbAdjustment.NOOP);

    const overlayService: NbOverlayService = TestBed.get(NbOverlayService);
    const overlayRef = overlayService.create({ positionStrategy: strategy });
    overlayRef.attach(new NbComponentPortal(PortalComponent));

    expect(withPositionsSpy).toHaveBeenCalledTimes(1);
    expect(withPositionsSpy).toHaveBeenCalledWith(jasmine.objectContaining([{
      originX: 'start',
      originY: 'center',
      overlayX: 'end',
      overlayY: 'center',
      offsetX: -15,
    }]));
  });

it('should apply center positions first', () => {
    const withPositionsSpy = spyOn(strategy, 'withPositions').and.callThrough();

    strategy.position(NbPosition.START).adjustment(NbAdjustment.CLOCKWISE);

    const overlayService: NbOverlayService = TestBed.get(NbOverlayService);
    const overlayRef = overlayService.create({ positionStrategy: strategy });
    overlayRef.attach(new NbComponentPortal(PortalComponent));

    expect(withPositionsSpy).toHaveBeenCalledWith(jasmine.objectContaining([
      { originX: 'start', originY: 'center', overlayX: 'end', overlayY: 'center', offsetX: -15 },
      { originX: 'start', originY: 'top', overlayX: 'end', overlayY: 'top', offsetX: -15 },
      { originX: 'start', originY: 'bottom', overlayX: 'end', overlayY: 'bottom', offsetX: -15 },
      { originX: 'center', originY: 'top', overlayX: 'center', overlayY: 'bottom', offsetY: -15 },
      { originX: 'end', originY: 'top', overlayX: 'end', overlayY: 'bottom', offsetY: -15 },
      { originX: 'start', originY: 'top', overlayX: 'start', overlayY: 'bottom', offsetY: -15 },
      { originX: 'end', originY: 'center', overlayX: 'start', overlayY: 'center', offsetX: 15 },
      { originX: 'end', originY: 'bottom', overlayX: 'start', overlayY: 'bottom', offsetX: 15 },
      { originX: 'end', originY: 'top', overlayX: 'start', overlayY: 'top', offsetX: 15 },
      { originX: 'center', originY: 'bottom', overlayX: 'center', overlayY: 'top', offsetY: 15 },