testEnterDocument() {
    control.render(sandbox);
    assertTrue('Control must be in the document', control.isInDocument());
    assertEquals(
        'Control must have 5 mouse and 3 key event listeners', 8,
        getListenerCount(control));
    assertEquals(
        'Control\'s key event handler must be attached to its ' +
            'key event target',
        control.getKeyEventTarget(), control.getKeyHandler().element_);
  }
Tests {@link Control#enterDocument}.
@suppress {visibility} suppression
     added to enable type checking