public void HasVertex()
{
var graph = new DiGraph <int, int>(1);
graph.AddEdge(1, 2);
graph.AddEdge(2, 3);
graph.AddEdge(3, 4);
graph.AddEdge(4, 5);
graph.AddEdge(5, 6);
graph.AddEdge(6, 7);
graph.AddVertex(99);
Assert.IsTrue(graph.HasVertex(1));
Assert.IsTrue(graph.HasVertex(2));
Assert.IsTrue(graph.HasVertex(3));
Assert.IsTrue(graph.HasVertex(4));
Assert.IsTrue(graph.HasVertex(5));
Assert.IsTrue(graph.HasVertex(6));
Assert.IsTrue(graph.HasVertex(7));
Assert.IsTrue(graph.HasVertex(99));
Assert.IsFalse(graph.HasVertex(8));
}