public void TwinGraphCreatedFromGraphHasAllTwinVerticesBasedOnPrecursors()
 {
     Assert.AreEqual(2, _tg.Vertices.Count);
     Assert.IsTrue(VertexHelper.DoesTwinVertexExist(_v1.Guid, _tg.Vertices));
     Assert.IsTrue(VertexHelper.DoesTwinVertexExist(_v2.Guid, _tg.Vertices));
 }