* The performance of these calls on the underlying network. If the network’s performance isn’t sufficient, you need to either improve the network or use less of it.

### EventListener

  public void validateUndirectedEdges() {
    for (Integer node : network.nodes()) {
      new EqualsTester()
          .addEqualityGroup(
              network.inEdges(node), network.outEdges(node), network.incidentEdges(node))
          .testEquals();
      new EqualsTester()
          .addEqualityGroup(
              network.predecessors(node), network.successors(node), network.adjacentNodes(node))
          .testEquals();

        assertThat(network.incidentEdges(node).size() + selfLoopCount)
            .isEqualTo(network.inDegree(node) + network.outDegree(node));
        assertThat(network.inEdges(node)).hasSize(network.inDegree(node));
        assertThat(network.outEdges(node)).hasSize(network.outDegree(node));
      } else {
        assertThat(network.predecessors(node)).isEqualTo(network.adjacentNodes(node));

    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.incidentEdges(N1)).containsExactly(E11);
  }

  @Test
  public void incidentNodes_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.incidentNodes(E11).source()).isEqualTo(N1);
    assertThat(network.incidentNodes(E11).target()).isEqualTo(N1);
  }

    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.incidentEdges(N1)).containsExactly(E11);
  }

  @Test
  public void incidentNodes_selfLoop() {
    assume().that(network.allowsSelfLoops()).isTrue();

    addEdge(N1, N1, E11);
    assertThat(network.incidentNodes(E11).source()).isEqualTo(N1);
    assertThat(network.incidentNodes(E11).target()).isEqualTo(N1);
  }

      MutableNetwork<Integer, Object> network =
          networkBuilder.allowsParallelEdges(true).allowsSelfLoops(true).build();

      assertThat(network.nodes()).isEmpty();
      assertThat(network.edges()).isEmpty();
      AbstractNetworkTest.validateNetwork(network);

      while (network.nodes().size() < NUM_NODES) {
        network.addNode(gen.nextInt(NODE_POOL_SIZE));
      }

    addEdges(network);

    assertThat(network.edgeOrder()).isEqualTo(ElementOrder.insertion());
    assertThat(network.edges()).containsExactly("i", "e", "p").inOrder();
    assertThat(network.nodeOrder()).isEqualTo(ElementOrder.insertion()); // default
  }

  // The default ordering is INSERTION unless otherwise specified.
  @Test
  public void edgeOrder_default() {

    network.addEdge(N1, N1, E11);
    network.addEdge(N1, N1, E11_A);
    assertThat(network.edgesConnecting(N1, N1)).containsExactly(E11, E11_A);
  }

  private static class NetworkForTest<N, E> extends AbstractNetwork<N, E> {
    private final Network<N, E> network;

    NetworkForTest(Network<N, E> network) {
      this.network = network;
    }

  /**
   * Returns a view of {@code network} with the direction (if any) of every edge reversed. All other
   * properties remain intact, and further updates to {@code network} will be reflected in the view.
   */
  public static <N, E> Network<N, E> transpose(Network<N, E> network) {
    if (!network.isDirected()) {
      return network; // the transpose of an undirected network is an identical network
    }

  /**
   * Returns a view of {@code network} with the direction (if any) of every edge reversed. All other
   * properties remain intact, and further updates to {@code network} will be reflected in the view.
   */
  public static <N, E> Network<N, E> transpose(Network<N, E> network) {
    if (!network.isDirected()) {
      return network; // the transpose of an undirected network is an identical network
    }