Function createTrackByTestComponent

src/cdk/tree/tree.spec.ts:543–563

(trackByStrategy: 'reference' | 'property' | 'index')

      let component: CdkTreeAppWithTrackBy;

      function createTrackByTestComponent(trackByStrategy: 'reference' | 'property' | 'index') {
        fixture = TestBed.createComponent(CdkTreeAppWithTrackBy);
        component = fixture.componentInstance;
        component.trackByStrategy = trackByStrategy;
        fixture.detectChanges();

        dataSource = component.dataSource as FakeDataSource;
        tree = component.tree;
        treeElement = fixture.nativeElement.querySelector('cdk-tree');

        // Each node receives an attribute 'initialIndex' the element's original place
        getNodes(treeElement).forEach((node: Element, index: number) => {
          node.setAttribute('initialIndex', index.toString());
        });

        // Prove that the attributes match their indices
        const initialNodes = getNodes(treeElement);
        expect(initialNodes[0].getAttribute('initialIndex')).toBe('0');
        expect(initialNodes[1].getAttribute('initialIndex')).toBe('1');
        expect(initialNodes[2].getAttribute('initialIndex')).toBe('2');
      }

      function mutateData() {
        // Swap first and second data in data array