testIsAttachTarget() {
    popup.render();
    // Before 'attach' is called.
    assertFalse(
        'Menu should not be attached to the element',
        popup.isAttachTarget(anchor));

    popup.attach(anchor);
    assertTrue(
        'Menu should be attached to the anchor', popup.isAttachTarget(anchor));

    popup.detach(anchor);
    assertFalse(
        'Menu is expected to be detached from the element',
        popup.isAttachTarget(anchor));
  }
Test the behavior of {@link PopupMenu.isAttachTarget}.
     @suppress {visibility} suppression added to enable type checking