MutableNetwork<Integer, String> undirectedGraph =
        NetworkBuilder.undirected().allowsParallelEdges(true).allowsSelfLoops(true).build();
    undirectedGraph.addEdge(N1, N1, E11);
    undirectedGraph.addEdge(N1, N2, E12);
    undirectedGraph.addEdge(N1, N1, E11_A);
    undirectedGraph.addEdge(N1, N2, E12_A);
    undirectedGraph.addEdge(N2, N1, E21);

    return undirectedGraph;
  }

    assertThat(toString).contains("valueA");
    assertThat(toString).contains("valueB");
    assertThat(toString).contains("valueC");
    assertThat(toString).contains("valueD");
  }

  @Test
  public void undirectedGraph() {
    graph = ValueGraphBuilder.undirected().allowsSelfLoops(true).build();
    graph.putEdgeValue(1, 2, "valueA");
    graph.putEdgeValue(2, 1, "valueB"); // overwrites valueA in undirected case

    assertThat(toString).contains("valueA");
    assertThat(toString).contains("valueB");
    assertThat(toString).contains("valueC");
    assertThat(toString).contains("valueD");
  }

  @Test
  public void undirectedGraph() {
    graph = ValueGraphBuilder.undirected().allowsSelfLoops(true).build();
    graph.putEdgeValue(1, 2, "valueA");
    graph.putEdgeValue(2, 1, "valueB"); // overwrites valueA in undirected case