for (int trial = 0; trial < NUM_TRIALS; ++trial) {
      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) {

   * to add a self-loop to a graph that does not allow them will throw an {@link
   * IllegalArgumentException}.
   */
  @Override
  boolean allowsSelfLoops();

  /** Returns the order of iteration for the elements of {@link #nodes()}. */
  @Override
  ElementOrder<N> nodeOrder();

  /**

   * to add a self-loop to a graph that does not allow them will throw an {@link
   * IllegalArgumentException}.
   */
  @Override
  boolean allowsSelfLoops();

  /** Returns the order of iteration for the elements of {@link #nodes()}. */
  @Override
  ElementOrder<N> nodeOrder();

  /**

   * to add a self-loop to a graph that does not allow them will throw an {@link
   * IllegalArgumentException}.
   */
  @Override
  boolean allowsSelfLoops();

  /** Returns the order of iteration for the elements of {@link #nodes()}. */
  @Override
  ElementOrder<N> nodeOrder();

  /**