### Question:
DomainTreeModel implements TreeModel { public Object getRoot() { return d_root; } DomainTreeModel(Domain domain); Object getChild(Object parent, int childIndex); int getChildCount(Object parent); int getIndexOfChild(Object parent, Object child); Object getRoot(); boolean isLeaf(Object node); TreePath getPathTo(Object node); void addTreeModelListener(TreeModelListener listener); void removeTreeModelListener(TreeModelListener listener); void valueForPathChanged(TreePath path, Object node);  }### Answer:
@Test public void testGetRoot() { assertNotNull(d_treeModel.getRoot()); assertNotNull(d_treeModel.getRoot().toString()); }