testHighlightFirstOnOpen() {
    const node = dom.getElement('demoMenuButton');
    menuButton.decorate(node);
    menuButton.handleKeyEvent(new MyFakeEvent(KeyCodes.ENTER));
    assertEquals(
        'By default no items should be highlighted when opened with enter.',
        null, menuButton.getMenu().getHighlighted());

    menuButton.setOpen(false);
    menuButton.handleKeyEvent(new MyFakeEvent(KeyCodes.DOWN));
    assertTrue('Menu must open after down key', menuButton.isOpen());
    assertEquals(
        'First menuitem must be highlighted', 'menuItem1',
        menuButton.getMenu().getHighlighted().getElement().id);
  }
Check that the appropriate items are selected when menus are opened with
the keyboard and setSelectFirstOnEnterOrSpace is not set.
@suppress {checkTypes} suppression added to enable type checking