}

  @Test
  public void hasEdgeConnecting_directed_correct() {
    graph = ValueGraphBuilder.directed().build();
    graph.putEdgeValue(1, 2, "A");
    assertThat(graph.hasEdgeConnecting(EndpointPair.ordered(1, 2))).isTrue();
  }

  @Test
  public void hasEdgeConnecting_directed_backwards() {
    graph = ValueGraphBuilder.directed().build();
    graph.putEdgeValue(1, 2, "A");

  private static final ImmutableNetwork<String, String> IMMUTABLE_NETWORK_B =
      NetworkBuilder.directed().<String, String>immutable().addNode("B").build();

  public PackageSanityTests() {
    MutableNetwork<String, String> mutableNetworkA = NetworkBuilder.directed().build();
    mutableNetworkA.addNode("a");
    MutableNetwork<String, String> mutableNetworkB = NetworkBuilder.directed().build();

  }

  @Test
  public void hasEdgeConnecting_directed_correct() {
    graph = ValueGraphBuilder.directed().build();
    graph.putEdgeValue(1, 2, "A");
    assertThat(graph.hasEdgeConnecting(EndpointPair.ordered(1, 2))).isTrue();
  }

  @Test
  public void hasEdgeConnecting_directed_backwards() {
    graph = ValueGraphBuilder.directed().build();
    graph.putEdgeValue(1, 2, "A");

   * that edge to {@code value} (overwriting the existing value, if any).
   *
   * <p>If the graph is directed, the resultant edge will be directed; otherwise, it will be
   * undirected.
   *
   * <p>If this graph is directed, {@code endpoints} must be ordered.
   *
   * <p>Values do not have to be unique. However, values must be non-null.
   *

  public void transitiveClosure_directedGraph() {
    MutableGraph<Integer> directedGraph = GraphBuilder.directed().allowsSelfLoops(false).build();
    directedGraph.putEdge(N1, N2);
    directedGraph.putEdge(N1, N3);
    directedGraph.putEdge(N2, N3);
    directedGraph.addNode(N4);

    MutableGraph<Integer> expectedClosure = GraphBuilder.directed().allowsSelfLoops(true).build();
    expectedClosure.putEdge(N1, N1);
    expectedClosure.putEdge(N1, N2);

        ImmutableNetwork.copyOf(NetworkBuilder.directed().<String, String>build());
    Network<String, String> network2 = ImmutableNetwork.copyOf(network1);

    assertThat(network2).isSameInstanceAs(network1);
  }

  @Test
  public void edgesConnecting_directed() {
    MutableNetwork<String, String> mutableNetwork =
        NetworkBuilder.directed().allowsSelfLoops(true).build();

   *     false, creates an instance for graphs whose edges are each undirected.
   */
  AbstractGraphBuilder(boolean directed) {
    this.directed = directed;
  }

  /**
   * Adds {@code edge} connecting {@code endpoints}. In an undirected network, {@code edge} will
   * also connect {@code nodeV} to {@code nodeU}.
   *
   * <p>If this graph is directed, {@code edge} will be directed in this graph; if it is undirected,
   * {@code edge} will be undirected in this graph.
   *
   * <p>If this graph is directed, {@code endpoints} must be ordered.
   *

    Graph<String> graph1 = ImmutableGraph.copyOf(GraphBuilder.directed().<String>build());
    Graph<String> graph2 = ImmutableGraph.copyOf(graph1);

    assertThat(graph2).isSameInstanceAs(graph1);
  }

  @Test
  public void immutableGraphBuilder_appliesGraphBuilderConfig() {
    ImmutableGraph<String> emptyGraph =
        GraphBuilder.directed()
            .allowsSelfLoops(true)

    successorIterator = graph.successors(node).iterator();
    return true;
  }

  /**
   * If the graph is directed, each ordered [source, target] pair will be visited once if there is
   * an edge connecting them.
   */
  private static final class Directed<N> extends EndpointPairIterator<N> {
    private Directed(BaseGraph<N> graph) {
      super(graph);
    }

    @Override
    @CheckForNull