testRenderMenuAsSiblingForDecoratedButton() {
    const menu = new Menu();
    menu.addChild(new MenuItem('Menu item 1'), true /* render */);
    menu.addChild(new MenuItem('Menu item 2'), true /* render */);
    menu.addChild(new MenuItem('Menu item 3'), true /* render */);

    const menuButton = new MenuButton();
    menuButton.setMenu(menu);
    menuButton.setRenderMenuAsSibling(true);
    const node = dom.getElement('button1');
    menuButton.decorate(node);

    menuButton.setOpen(true);

    assertEquals(
        'The menu should be rendered immediately after the menu button',
        dom.getNextElementSibling(menuButton.getElement()), menu.getElement());

    assertEquals(
        'The menu should be rendered immediately before the next button',
        dom.getNextElementSibling(menu.getElement()),
        dom.getElement('button2'));
  }
Check that we render the menu as a sibling of the menu button, immediately
after the menu button.