testSubmenuSelectable() {
    const submenu = new SubMenu('submenu');
    submenu.addItem(new MenuItem('submenu item 1'));
    menu.addItem(submenu);
    submenu.setSelectable(true);

    let numClicks = 0;
    const menuClickedFn = (e) => {
      numClicks++;
    };

    events.listen(submenu, Component.EventType.ACTION, menuClickedFn);
    submenu.performActionInternal(null);
    submenu.performActionInternal(null);

    assertEquals('The submenu should have fired an event', 2, numClicks);

    submenu.setSelectable(false);
    submenu.performActionInternal(null);

    assertEquals(
        'The submenu should not have fired any further events', 2, numClicks);
  }
Tests that if a sub menu is selectable, then it can handle actions.
     @suppress {visibility} suppression added to enable type checking