DOMUtils domUtils = frame.getDOMUtils();
//
Object rootPanel = objectUtils.getRootPanel();
Object rootPanelElement = objectUtils.getElement(rootPanel);
// when RootPanel is live, we have much of Element's
domUtils.appendChild(rootPanelElement, domUtils.createButton());
{
int count = domUtils.getChildCount(rootPanelElement);
assertThat(count).isGreaterThan(1);
}
// dispose, so now RootPanel should be empty