private static string SerializeGraph1([NotNull] TestGraph graph)
        {
            string filePath = Path.Combine(
                GetTemporaryTestDirectory(),
                $"serialization_to_graphml_test_{Guid.NewGuid().ToString()}.graphml");

            graph.SerializeToGraphML <TestVertex, TestEdge, TestGraph>(filePath);
            Assert.IsTrue(File.Exists(filePath));
            return(File.ReadAllText(filePath));
        }
        private static string SerializeGraph3([NotNull] TestGraph graph)
        {
            using (var writer = new StringWriter())
            {
                var settings = new XmlWriterSettings {
                    Indent = true
                };
                using (XmlWriter xmlWriter = XmlWriter.Create(writer, settings))
                {
                    graph.SerializeToGraphML <TestVertex, TestEdge, TestGraph>(xmlWriter);
                }

                return(writer.ToString());
            }
        }