testAttachEventTarget1() {
    const target = new GoogEventTarget();

    assertNull(mh.activeElement_);
    mh.attachInput(target);
    assertNull(mh.activeElement_);

    mockElement.dispatchEvent(new GoogEvent('focus', mockElement));
    assertEquals(mockElement, mh.activeElement_);

    mh.detachInput(target);
  }
Check attaching to an EventTarget instead of an element.
     @suppress {visibility} suppression added to enable type checking