public void Test_AddAttribute()
        {
            GraphVizProcessor gvp = new GraphVizProcessor();

            gvp.graph = new Graph(GraphType.Digraph, new Stmt_list());

            //Graph, Node, Edge attribute
            gvp.AddAttribute(AttrType.Graph, new IDisID("x", "y"));
            string tmp = gvp.graph.ToCode();

            if (!tmp.Contains("graph [x=y;]"))
            {
                Assert.Fail("Attr_stmt type attribute not found.");
            }

            //Specific node attribute
            gvp.AddNode("a");
            gvp.AddAttribute(AttrType.SpecificNode, new IDisID("x", "y"), "a");
            tmp = gvp.graph.ToCode();
            if (!tmp.Contains("a [x=y;]"))
            {
                Assert.Fail("Node attribute not found.");
            }

            //Specific node attribute
            gvp.AddEdge("a", "b");
            gvp.AddAttribute(AttrType.SpecificEdge, new IDisID("x", "y"), "a", "b");
            tmp = gvp.graph.ToCode();
            if (!tmp.Contains("a -> b [x=y;]"))
            {
                Assert.Fail("Edge attribute not found.");
            }
        }