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();

   * 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.
   *

    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

  private GraphBuilder(boolean directed) {
    super(directed);
  }

  /** Returns a {@link GraphBuilder} for building directed graphs. */
  public static GraphBuilder<Object> directed() {
    return new GraphBuilder<>(true);
  }

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

  /**

    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)

  private final EdgeType edgeType;
  private final MutableGraph<Integer> graph;

  // add parameters: directed/undirected
  @Parameters
  public static Collection<Object[]> parameters() {
    return Arrays.asList(new Object[][] {{EdgeType.UNDIRECTED}, {EdgeType.DIRECTED}});
  }

  public GraphEquivalenceTest(EdgeType edgeType) {
    this.edgeType = edgeType;
    this.graph = createGraph(edgeType);
  }

  // Node order tests

  @Test
  public void nodeOrder_none() {
    MutableGraph<Integer> graph = GraphBuilder.directed().nodeOrder(unordered()).build();

    assertThat(graph.nodeOrder()).isEqualTo(unordered());
  }

  @Test
  public void nodeOrder_insertion() {
    MutableGraph<Integer> graph = GraphBuilder.directed().nodeOrder(insertion()).build();

    addNodes(graph);

    assertThat(graph.nodeOrder()).isEqualTo(insertion());

        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();

        new Object[][] {
          {UNDIRECTED}, {DIRECTED},
        });
  }

  private final EdgeType 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();

        ImmutableValueGraph.copyOf(ValueGraphBuilder.directed().<String, Integer>build());
    ValueGraph<String, Integer> graph2 = ImmutableValueGraph.copyOf(graph1);

    assertThat(graph2).isSameInstanceAs(graph1);
  }

  @Test
  public void incidentEdgeOrder_stable() {
    ImmutableValueGraph<String, Integer> immutableValueGraph =
        ImmutableValueGraph.copyOf(ValueGraphBuilder.directed().<String, Integer>build());