Method observe

lib/utils/test/mockResizeObserver.ts:84–91

(element: HTMLElement)

  }

  observe(element: HTMLElement) {
    if (this.#disconnected) {
      return;
    }

    this.#elements.add(element);
    this.#notify([element]);
  }

  unobserve(element: HTMLElement) {
    this.#elements.delete(element);