* subtype of {@code ValueGraph} that provides methods for adding and removing nodes and edges. If
 * you do not need to mutate a graph (e.g. if you write a method than runs a read-only algorithm on
 * the graph), you should use the non-mutating {@link ValueGraph} interface, or an {@link
 * ImmutableValueGraph}.
 *
 * <p>You can create an immutable copy of an existing {@code ValueGraph} using {@link

    return newBuilder;
  }

  /**
   * Specifies the order of iteration for the elements of {@link ValueGraph#edges()}, {@link
   * ValueGraph#adjacentNodes(Object)}, {@link ValueGraph#predecessors(Object)}, {@link
   * ValueGraph#successors(Object)} and {@link ValueGraph#incidentEdges(Object)}.
   *
   * <p>The default value is {@link ElementOrder#unordered() unordered} for mutable graphs. For

    };
  }

  @Override
  public final boolean equals(@CheckForNull Object obj) {
    if (obj == this) {
      return true;
    }
    if (!(obj instanceof ValueGraph)) {
      return false;
    }
    ValueGraph<?, ?> other = (ValueGraph<?, ?>) obj;

    return isDirected() == other.isDirected()
        && nodes().equals(other.nodes())
        && edgeValueMap(this).equals(edgeValueMap(other));
  }

  public void copyOf_directedValueGraph() {
    ValueGraph<Integer, String> directedGraph = buildDirectedValueGraph();

    ValueGraph<Integer, String> copy = copyOf(directedGraph);
    assertThat(copy).isEqualTo(directedGraph);
  }

  @Test
  public void copyOf_undirectedValueGraph() {
    ValueGraph<Integer, String> undirectedGraph = buildUndirectedValueGraph();

    ValueGraph<Integer, String> copy = copyOf(undirectedGraph);

  private static class TransposedValueGraph<N, V> extends ForwardingValueGraph<N, V> {
    private final ValueGraph<N, V> graph;

    TransposedValueGraph(ValueGraph<N, V> graph) {
      this.graph = graph;
    }

    @Override
    ValueGraph<N, V> delegate() {
      return graph;
    }

    @Override
    public Set<N> predecessors(N node) {

    MutableValueGraph<String, Integer> valueGraph = ValueGraphBuilder.directed().build();
    valueGraph.putEdgeValue("a", "b", 11);

    Traverser.forTree(valueGraph); // Does not throw
  }

  @Test
  public void forTree_withUndirectedValueGraph_throws() throws Exception {
    MutableValueGraph<String, Integer> valueGraph = ValueGraphBuilder.undirected().build();
    valueGraph.putEdgeValue("a", "b", 11);

  public void copyOf_directedValueGraph() {
    ValueGraph<Integer, String> directedGraph = buildDirectedValueGraph();

    ValueGraph<Integer, String> copy = copyOf(directedGraph);
    assertThat(copy).isEqualTo(directedGraph);
  }

  @Test
  public void copyOf_undirectedValueGraph() {
    ValueGraph<Integer, String> undirectedGraph = buildUndirectedValueGraph();

    ValueGraph<Integer, String> copy = copyOf(undirectedGraph);

    assertThat(graphA.nodeOrder()).isEqualTo(graphB.nodeOrder());

    assertThat(graphA).isEqualTo(graphB);
  }

  static void assertStronglyEquivalent(ValueGraph<?, ?> graphA, ValueGraph<?, ?> graphB) {
    // Properties not covered by equals()
    assertThat(graphA.allowsSelfLoops()).isEqualTo(graphB.allowsSelfLoops());
    assertThat(graphA.nodeOrder()).isEqualTo(graphB.nodeOrder());

    assertThat(graphA.nodeOrder()).isEqualTo(graphB.nodeOrder());

    assertThat(graphA).isEqualTo(graphB);
  }

  static void assertStronglyEquivalent(ValueGraph<?, ?> graphA, ValueGraph<?, ?> graphB) {
    // Properties not covered by equals()
    assertThat(graphA.allowsSelfLoops()).isEqualTo(graphB.allowsSelfLoops());
    assertThat(graphA.nodeOrder()).isEqualTo(graphB.nodeOrder());

  static final String ENDPOINTS_MISMATCH =
      "Mismatch: endpoints' ordering is not compatible with directionality of the graph";

  /** Singleton edge value for {@link Graph} implementations backed by {@link ValueGraph}s. */
  enum Presence {
    EDGE_EXISTS
  }