private static void AssertGraphsEqual(
     IEdgeListGraph <int, Edge <int> > g,
     IEdgeListGraph <int, Edge <int> > result)
 {
     // check equal
     Assert.IsTrue(GraphContract.VertexCountEqual(g, result));
     Assert.IsTrue(GraphContract.EdgeCountEqual(g, result));
     foreach (var v in g.Vertices)
     {
         Assert.IsTrue(result.ContainsVertex(v));
     }
     //foreach (var e in g.Edges)
     //    Assert.IsTrue(result.ContainsEdge(e.Source, e.Target));
 }