EndpointPair.ordered(N4, N4));
  }

  @Test
  public void endpointPair_undirectedNetwork() {
    MutableNetwork<Integer, String> undirectedNetwork =
        NetworkBuilder.undirected().allowsParallelEdges(true).allowsSelfLoops(true).build();
    undirectedNetwork.addNode(N0);
    undirectedNetwork.addEdge(N1, N2, E12);
    undirectedNetwork.addEdge(N2, N1, E12_A); // adds parallel edge, won't be in Graph edges

        EndpointPair.ordered(N4, N4));
  }

  @Test
  public void endpointPair_undirectedNetwork() {
    MutableNetwork<Integer, String> undirectedNetwork =
        NetworkBuilder.undirected().allowsParallelEdges(true).allowsSelfLoops(true).build();
    undirectedNetwork.addNode(N0);
    undirectedNetwork.addEdge(N1, N2, E12);
    undirectedNetwork.addEdge(N2, N1, E12_A); // adds parallel edge, won't be in Graph edges

    // In a directed graph, parallel edges cannot introduce a cycle in an acyclic graph.
    // However, in an undirected graph, any parallel edge induces a cycle in the graph.
    if (!network.isDirected()
        && network.allowsParallelEdges()
        && network.edges().size() > network.asGraph().edges().size()) {
      return true;
    }
    return hasCycle(network.asGraph());
  }

  /**