public void TopologicalSortTest()
        {
            for (int n = 0; n < 5; n++)
            {
                Vertex[] vertices = TopologicalSortTestClass.CreateDirectedAcyclicGraph(n);
                Vertex[] order    = TopologicalSort.Run(vertices);

                for (int i = n - 1; i >= 0; i--)
                {
                    foreach (Vertex v in vertices)
                    {
                        v.Reset();
                    }

                    DepthFirstSearch.Run(order[i]);
                    for (int j = 0; j < i; j++)
                    {
                        Assert.AreEqual(Color.White, order[j].Color);
                    }
                }
            }
        }