internal void Graph_OutEdgesShouldHaveSameTail(GraphDefinitionParameter p)
        {
            // Arrange
            using MutableUndirectedSimpleIncidenceGraph builder = new(p.VertexCount);
            foreach (Endpoints endpoints in p.Edges)
            {
                builder.Add(endpoints.Tail, endpoints.Head);
            }

            Graph graph = builder.ToGraph();

            // Act
            for (int vertex = 0; vertex < graph.VertexCount; ++vertex)
            {
                EdgeEnumerator outEdges = graph.EnumerateOutEdges(vertex);
                while (outEdges.MoveNext())
                {
                    Endpoints edge    = outEdges.Current;
                    bool      hasTail = graph.TryGetTail(edge, out int tail);
                    if (!hasTail)
                    {
                        Assert.True(hasTail);
                    }

                    // Assert
                    Assert.Equal(vertex, tail);
                }
            }
        }
        private static bool TryGetEndpoints(Graph graph, Endpoints edge, out Endpoints endpoints)
        {
            bool hasTail = graph.TryGetTail(edge, out int tail);
            bool hasHead = graph.TryGetHead(edge, out int head);

            endpoints = new Endpoints(tail, head);
            return(hasTail && hasHead);
        }