Tree extends Composite implements HasSelectionHandlers<T>,
                                                                   HasOpenHandlers<T>,
                                                                   HasCloseHandlers<T> { public boolean isEmpty() { return container.getWidgetCount() == 0; } Tree();   Tree(final Supplier<FlowPanel> containerProvider); @Override HandlerRegistration addOpenHandler(final OpenHandler<T> handler); @Override HandlerRegistration addCloseHandler(final CloseHandler<T> handler); @Override HandlerRegistration addSelectionHandler(final SelectionHandler<T> handler); void clear(); void setSelectedItem(final T item,
                                final boolean fireEvents); T getSelectedItem(); void setSelectedItem(final T item); @SuppressWarnings("unchecked") T addItem(final T item); @SuppressWarnings("unchecked") T getItemByUuid(String uuid); T getItem(int index); void removeItem(final T item); Iterable<T> getItems(); boolean isEmpty();  }
@Test public void testIsEmpty() { assertEquals(testedTree.isEmpty(), true); }