public static NetworkBuilder<Object, Object> directed() {
    return new NetworkBuilder<>(true);
  }

  /** Returns a {@link NetworkBuilder} for building undirected networks. */
  public static NetworkBuilder<Object, Object> undirected() {
    return new NetworkBuilder<>(false);
  }

  /**
   * Returns a {@link NetworkBuilder} initialized with all properties queryable from {@code
   * network}.

  }

  /**
   * Tests that the ImmutableNetwork.Builder doesn't change when the creating NetworkBuilder
   * changes.
   */
  @Test
  @SuppressWarnings("CheckReturnValue")
  public void immutableNetworkBuilder_copiesNetworkBuilder() {
    NetworkBuilder<String, Object> networkBuilder =
        NetworkBuilder.directed()
            .allowsSelfLoops(true)
            .<String>nodeOrder(ElementOrder.<String>natural());

  Network<Integer, String> createGraph() {
    networkBuilder =
        NetworkBuilder.directed()
            .allowsSelfLoops(allowsSelfLoops)
            .allowsParallelEdges(allowsParallelEdges)
            .nodeOrder(nodeOrder)
            .edgeOrder(edgeOrder)
            .immutable();

    return networkBuilder.build();
  }

  @Override
  void addNode(Integer n) {
    networkBuilder.addNode(n);

  private static final NetworkBuilder<?, ?> networkBuilderA =
      NetworkBuilder.directed().allowsParallelEdges(true).expectedNodeCount(10);
  private static final NetworkBuilder<?, ?> networkBuilderB =
      NetworkBuilder.directed().allowsSelfLoops(true).expectedNodeCount(16);

  private static final ImmutableNetwork<String, String> IMMUTABLE_NETWORK_A =

  @Test
  public void directedNetwork() {
    testNetworkMutation(NetworkBuilder.directed());
  }

  @Test
  public void undirectedNetwork() {
    testNetworkMutation(NetworkBuilder.undirected());
  }

  private static void testNetworkMutation(NetworkBuilder<? super Integer, Object> networkBuilder) {
    Random gen = new Random(42); // Fixed seed so test results are deterministic.

   * before it.
   *
   * @since 28.0
   */
  public static class Builder<N, E> {

    private final MutableNetwork<N, E> mutableNetwork;

    Builder(NetworkBuilder<N, E> networkBuilder) {
      this.mutableNetwork = networkBuilder.build();
    }

    /**
     * Adds {@code node} if it is not already present.
     *

  }

  /**
   * Tests that the ImmutableNetwork.Builder doesn't change when the creating NetworkBuilder
   * changes.
   */
  @Test
  @SuppressWarnings("CheckReturnValue")
  public void immutableNetworkBuilder_copiesNetworkBuilder() {
    NetworkBuilder<String, Object> networkBuilder =
        NetworkBuilder.directed()
            .allowsSelfLoops(true)
            .<String>nodeOrder(ElementOrder.<String>natural());

  Network<Integer, String> createGraph() {
    networkBuilder =
        NetworkBuilder.directed()
            .allowsSelfLoops(allowsSelfLoops)
            .allowsParallelEdges(allowsParallelEdges)
            .nodeOrder(nodeOrder)
            .edgeOrder(edgeOrder)
            .immutable();

    return networkBuilder.build();
  }

  @Override
  void addNode(Integer n) {
    networkBuilder.addNode(n);

  private static final NetworkBuilder<?, ?> networkBuilderA =
      NetworkBuilder.directed().allowsParallelEdges(true).expectedNodeCount(10);
  private static final NetworkBuilder<?, ?> networkBuilderB =
      NetworkBuilder.directed().allowsSelfLoops(true).expectedNodeCount(16);

  private static final ImmutableNetwork<String, String> IMMUTABLE_NETWORK_A =

  public DefaultNetworkImplementationsTest(EdgeType edgeType) {
    this.edgeType = edgeType;
  }

  @Before
  public void setUp() throws Exception {
    NetworkBuilder<Object, Object> builder =
        (edgeType == EdgeType.DIRECTED) ? NetworkBuilder.directed() : NetworkBuilder.undirected();

    network = builder.allowsSelfLoops(true).allowsParallelEdges(true).build();
    networkForTest = NetworkForTest.from(network);
  }

  @Test