public void DiGraph_Smoke_Test()
        {
            var graph = new DiGraph <int>();

            graph.AddVertex(1);
            graph.AddVertex(2);
            graph.AddVertex(3);
            graph.AddVertex(4);
            graph.AddVertex(5);

            graph.AddEdge(1, 2);
            Assert.IsTrue(graph.HasEdge(1, 2));
            Assert.IsFalse(graph.HasEdge(2, 1));

            graph.AddEdge(3, 2);
            Assert.AreEqual(2, graph.InEdges(2).Count());
            graph.RemoveEdge(3, 2);

            graph.AddEdge(2, 3);
            graph.AddEdge(3, 4);
            graph.AddEdge(4, 5);
            graph.AddEdge(4, 1);
            graph.AddEdge(3, 5);

            Assert.AreEqual(2, graph.OutEdges(4).Count());

            Assert.AreEqual(5, graph.VerticesCount);

            Assert.IsTrue(graph.HasEdge(1, 2));

            graph.RemoveEdge(1, 2);

            Assert.IsFalse(graph.HasEdge(1, 2));

            graph.RemoveEdge(2, 3);
            graph.RemoveEdge(3, 4);
            graph.RemoveEdge(4, 5);
            graph.RemoveEdge(4, 1);

            Assert.IsTrue(graph.HasEdge(3, 5));
            graph.RemoveEdge(3, 5);
            Assert.IsFalse(graph.HasEdge(3, 5));

            graph.RemoveVertex(1);
            graph.RemoveVertex(2);
            graph.RemoveVertex(3);

            graph.AddEdge(4, 5);
            graph.RemoveVertex(4);

            graph.AddEdge(5, 5);
            graph.RemoveEdge(5, 5);
            graph.RemoveVertex(5);


            Assert.AreEqual(0, graph.VerticesCount);
        }