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());

   * 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());

import com.google.common.collect.ImmutableSet;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

/**
 * Standard implementation of {@link Network} that supports the options supplied by {@link
 * NetworkBuilder}.
 *
 * <p>This class maintains a map of nodes to {@link NetworkConnections}. This class also maintains a
 * map of edges to reference nodes. The reference node is defined to be the edge's source node on

 * create an instance of one of the built-in implementations of {@code Network}, use the {@link
 * NetworkBuilder} class:
 *
 * {@snippet :
 * MutableNetwork<Integer, MyEdge> network = NetworkBuilder.directed().build();
 * }
 *
 * <p>{@link NetworkBuilder#build()} returns an instance of {@link MutableNetwork}, which is a

    MutableNetwork<Integer, String> network =
        NetworkBuilder.directed().edgeOrder(unordered()).build();

    assertThat(network.edgeOrder()).isEqualTo(unordered());
    assertThat(network.nodeOrder()).isEqualTo(insertion()); // default
  }

  @Test
  public void edgeOrder_insertion() {
    MutableNetwork<Integer, String> network =
        NetworkBuilder.directed().edgeOrder(insertion()).build();

  }

  @Test
  public void testAdjacentNode_nodeNotIncident() {
    ImmutableList<MutableNetwork<Integer, String>> testNetworks =
        ImmutableList.of(
            NetworkBuilder.directed().<Integer, String>build(),
            NetworkBuilder.undirected().<Integer, String>build());
    for (MutableNetwork<Integer, String> network : testNetworks) {
      network.addEdge(1, 2, "1-2");

  }

  @Test
  public void testAdjacentNode_nodeNotIncident() {
    ImmutableList<MutableNetwork<Integer, String>> testNetworks =
        ImmutableList.of(
            NetworkBuilder.directed().<Integer, String>build(),
            NetworkBuilder.undirected().<Integer, String>build());
    for (MutableNetwork<Integer, String> network : testNetworks) {
      network.addEdge(1, 2, "1-2");

    MutableNetwork<Integer, String> undirectedGraph = NetworkBuilder.undirected().build();
    undirectedGraph.addEdge(N1, N2, E12);

    assertThat(transpose(undirectedGraph)).isSameInstanceAs(undirectedGraph);
  }

  @Test
  public void transpose_directedNetwork() {
    MutableNetwork<Integer, String> directedGraph =
        NetworkBuilder.directed().allowsParallelEdges(true).allowsSelfLoops(true).build();