Model graph = du.getModel() ;
assertTrue(graph.isEmpty()) ;
graph = du.getModel(gn1) ;
assertTrue(graph.isIsomorphicWith(model1)) ;
du.deleteModel(gn1) ;
exists = du.containsModel(gn1) ;
assertFalse("Expected gn1 not to exist", exists) ;
graph = du.getModel(gn1) ;
assertNull(graph) ;