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;
  }

    MutableGraph<Integer> undirectedGraph = GraphBuilder.undirected().allowsSelfLoops(true).build();
    undirectedGraph.addNode(N0);
    undirectedGraph.putEdge(N1, N2);
    undirectedGraph.putEdge(N2, N1); // does nothing
    undirectedGraph.putEdge(N1, N3);
    undirectedGraph.putEdge(N4, N4);
    containsExactlySanityCheck(
        undirectedGraph.edges(),
        EndpointPair.unordered(N1, N2),

  private static final int NODE_POOL_SIZE = 1000; // must be >> NUM_NODES

  @Test
  public void directedGraph() {
    testGraphMutation(GraphBuilder.directed());
  }

  @Test
  public void undirectedGraph() {
    testGraphMutation(GraphBuilder.undirected());
  }

  private static void testGraphMutation(GraphBuilder<? super Integer> graphBuilder) {

  private static final int NODE_POOL_SIZE = 1000; // must be >> NUM_NODES

  @Test
  public void directedGraph() {
    testGraphMutation(GraphBuilder.directed());
  }

  @Test
  public void undirectedGraph() {
    testGraphMutation(GraphBuilder.undirected());
  }

  private static void testGraphMutation(GraphBuilder<? super Integer> graphBuilder) {