testSetSelectedItemBeforeRender() {
    select.addItem(new MenuItem('item 1'));
    select.addItem(new MenuItem('item 2'));
    const item3 = new MenuItem('item 3');
    select.addItem(item3);
    select.setSelectedItem(item3);
    assertEquals(2, select.getSelectedIndex());

    select.decorate(sandboxEl);
    assertEquals(2, select.getSelectedIndex());
  }
Checks that if an item is selected before decorate is called, the selection
is preserved after decorate.