Vertices() {         DirectedMultigraph<String> g = new DirectedMultigraph<String>();         assertTrue(g.add(new SimpleDirectedTypedEdge<String>("type-0",0, 0)));         assertTrue(g.contains(new SimpleDirectedTypedEdge<String>("type-0",0, 0)));         assertTrue(g.add(new SimpleDirectedTypedEdge<String>("type-0",0, 0)));         assertTrue(g.contains(new SimpleDirectedTypedEdge<String>("type-0",0, 0)));         assertTrue(g.add(new SimpleDirectedTypedEdge<String>("type-0", 0, 0)));         assertTrue(g.contains(new SimpleDirectedTypedEdge<String>("type-0",0, 0)));          DirectedMultigraph<String> copy = g.copy(