MutableNetwork<Integer, String> directedGraph =
        NetworkBuilder.directed().allowsParallelEdges(true).allowsSelfLoops(true).build();
    directedGraph.addEdge(N1, N3, E13);
    directedGraph.addEdge(N3, N1, E31);
    directedGraph.addEdge(N1, N2, E12);
    directedGraph.addEdge(N1, N2, E12_A);
    directedGraph.addEdge(N1, N1, E11);
    directedGraph.addEdge(N3, N4, E34);

  public void endpointPair_directedGraph() {
    MutableGraph<Integer> directedGraph = GraphBuilder.directed().allowsSelfLoops(true).build();
    directedGraph.addNode(N0);
    directedGraph.putEdge(N1, N2);
    directedGraph.putEdge(N2, N1);
    directedGraph.putEdge(N1, N3);
    directedGraph.putEdge(N4, N4);
    containsExactlySanityCheck(
        directedGraph.edges(),
        EndpointPair.ordered(N1, N2),

  private static final int NUM_NODES = 100;
  private static final int NUM_EDGES = 1000;
  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 final int NUM_NODES = 100;
  private static final int NUM_EDGES = 1000;
  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());
  }