}

  /** Returns a string representation of this graph. */
  @Override
  public String toString() {
    return "isDirected: "
        + isDirected()
        + ", allowsSelfLoops: "
        + allowsSelfLoops()
        + ", nodes: "
        + nodes()
        + ", edges: "
        + edges();
  }

  }

  private static MutableGraph<Integer> createGraph(EdgeType edgeType) {
    switch (edgeType) {
      case UNDIRECTED:
        return GraphBuilder.undirected().allowsSelfLoops(true).build();
      case DIRECTED:
        return GraphBuilder.directed().allowsSelfLoops(true).build();
    }
    throw new IllegalStateException("Unexpected edge type: " + edgeType);
  }

  private static EdgeType oppositeType(EdgeType edgeType) {

    ImmutableGraph<String> emptyGraph =
        GraphBuilder.directed()
            .allowsSelfLoops(true)
            .nodeOrder(ElementOrder.<String>natural())
            .immutable()
            .build();

    assertThat(emptyGraph.isDirected()).isTrue();
    assertThat(emptyGraph.allowsSelfLoops()).isTrue();
    assertThat(emptyGraph.nodeOrder()).isEqualTo(ElementOrder.<String>natural());
  }

  /**

    ImmutableValueGraph<String, Integer> emptyGraph =
        ValueGraphBuilder.directed()
            .allowsSelfLoops(true)
            .nodeOrder(ElementOrder.<String>natural())
            .<String, Integer>immutable()
            .build();

    assertThat(emptyGraph.isDirected()).isTrue();
    assertThat(emptyGraph.allowsSelfLoops()).isTrue();
    assertThat(emptyGraph.nodeOrder()).isEqualTo(ElementOrder.<String>natural());
  }

  private static final AbstractGraphBuilder<?> graphBuilderA =
      GraphBuilder.directed().expectedNodeCount(10);
  private static final AbstractGraphBuilder<?> graphBuilderB =
      ValueGraphBuilder.directed().allowsSelfLoops(true).expectedNodeCount(16);

  private static final ImmutableGraph<String> IMMUTABLE_GRAPH_A =
      GraphBuilder.directed().<String>immutable().addNode("A").build();

    return delegate().edges().size();
  }

  @Override
  public boolean isDirected() {
    return delegate().isDirected();
  }

  @Override
  public boolean allowsSelfLoops() {
    return delegate().allowsSelfLoops();
  }

  @Override
  public ElementOrder<N> nodeOrder() {
    return delegate().nodeOrder();
  }

  @Override
  public ElementOrder<N> incidentEdgeOrder() {

    return delegate().edges().size();
  }

  @Override
  public boolean isDirected() {
    return delegate().isDirected();
  }

  @Override
  public boolean allowsSelfLoops() {
    return delegate().allowsSelfLoops();
  }

  @Override
  public ElementOrder<N> nodeOrder() {
    return delegate().nodeOrder();
  }

  @Override
  public ElementOrder<N> incidentEdgeOrder() {

   *     nodeV}, or null if there was no such edge.
   * @throws IllegalArgumentException if the introduction of the edge would violate {@link
   *     #allowsSelfLoops()}
   */
  @CanIgnoreReturnValue
  @Nullable V putEdgeValue(N nodeU, N nodeV, V value);

  /**
   * Adds an edge connecting {@code endpoints} if one is not already present, and sets a value for

    return delegate().isDirected();
  }

  @Override
  public boolean allowsParallelEdges() {
    return delegate().allowsParallelEdges();
  }

  @Override
  public boolean allowsSelfLoops() {
    return delegate().allowsSelfLoops();
  }

  @Override
  public ElementOrder<N> nodeOrder() {
    return delegate().nodeOrder();
  }

  @Override
  public ElementOrder<E> edgeOrder() {

  @Override
  @CanIgnoreReturnValue
  public @Nullable V putEdgeValue(N nodeU, N nodeV, V value) {
    checkNotNull(nodeU, "nodeU");
    checkNotNull(nodeV, "nodeV");
    checkNotNull(value, "value");

    if (!allowsSelfLoops()) {
      checkArgument(!nodeU.equals(nodeV), SELF_LOOPS_NOT_ALLOWED, nodeU);
    }

    GraphConnections<N, V> connectionsU = nodeConnections.get(nodeU);
    if (connectionsU == null) {