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();

  }

  private static MutableNetwork<Integer, String> createNetwork(EdgeType edgeType) {
    switch (edgeType) {
      case UNDIRECTED:
        return NetworkBuilder.undirected().allowsSelfLoops(true).build();
      case DIRECTED:
        return NetworkBuilder.directed().allowsSelfLoops(true).build();
      default:
        throw new IllegalStateException("Unexpected edge type: " + edgeType);
    }
  }

  @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.

    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();

  }

  private static MutableNetwork<Integer, String> createNetwork(EdgeType edgeType) {
    switch (edgeType) {
      case UNDIRECTED:
        return NetworkBuilder.undirected().allowsSelfLoops(true).build();
      case DIRECTED:
        return NetworkBuilder.directed().allowsSelfLoops(true).build();
      default:
        throw new IllegalStateException("Unexpected edge type: " + edgeType);
    }
  }

  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

   * 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.
     *

  }

  @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");

    this.allowsParallelEdges = allowsParallelEdges;
    this.nodeOrder = nodeOrder;
    this.edgeOrder = edgeOrder;
  }

  @Override
  MutableNetwork<Integer, String> createGraph() {
    return NetworkBuilder.directed()
        .allowsSelfLoops(allowsSelfLoops)
        .allowsParallelEdges(allowsParallelEdges)
        .nodeOrder(nodeOrder)
        .edgeOrder(edgeOrder)
        .build();
  }

  @Override