*
   * @return the value previously associated with the edge connecting {@code nodeU} to {@code
   *     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);

  /**

      mutableValueGraph.addNode(node);
      return this;
    }

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

    N previousNode = incidentEdgeMap.remove(edge);
    // We're relying on callers to call this method only with an edge that's in the graph.
    return requireNonNull(previousNode);
  }

  @Override
  public void addInEdge(E edge, N node, boolean isSelfLoop) {
    if (!isSelfLoop) {
      addOutEdge(edge, node);
    }
  }

  @Override
  public void addOutEdge(E edge, N node) {

      assertThat(network.incidentEdges(nodeV)).contains(edge);

      for (N incidentNode : network.incidentNodes(edge)) {
        assertThat(network.nodes()).contains(incidentNode);
        for (E adjacentEdge : network.incidentEdges(incidentNode)) {
          assertTrue(
              edge.equals(adjacentEdge) || network.adjacentEdges(edge).contains(adjacentEdge));
        }
      }
    }

    for (N node : graph.nodes()) {
      copy.addNode(node);
    }
    for (EndpointPair<N> edge : graph.edges()) {
      // requireNonNull is safe because the endpoint pair comes from the graph.
      copy.putEdgeValue(
          edge.nodeU(),
          edge.nodeV(),
          requireNonNull(graph.edgeValueOrDefault(edge.nodeU(), edge.nodeV(), null)));
    }
    return copy;
  }

    for (N node : graph.nodes()) {
      copy.addNode(node);
    }
    for (EndpointPair<N> edge : graph.edges()) {
      // requireNonNull is safe because the endpoint pair comes from the graph.
      copy.putEdgeValue(
          edge.nodeU(),
          edge.nodeV(),
          requireNonNull(graph.edgeValueOrDefault(edge.nodeU(), edge.nodeV(), null)));
    }
    return copy;
  }

      }
      Collections.shuffle(edgeList, gen);
      for (EndpointPair<Integer> edge : edgeList) {
        assertThat(graph.putEdge(edge.nodeU(), edge.nodeV())).isTrue();
      }

      assertThat(graph.nodes()).hasSize(NUM_NODES);
      assertThat(graph.edges()).hasSize(NUM_EDGES);
      AbstractGraphTest.validateGraph(graph);
    }
  }

  /**
   * Returns the value associated with the edge connecting the origin node to {@code node}, or null
   * if there is no such edge.
   */
  @Nullable V value(N node);

  /** Remove {@code node} from the set of predecessors. */
  void removePredecessor(N node);

  /**
   * Remove {@code node} from the set of successors. Returns the value previously associated with
   * the edge connecting the two nodes.
   */

  static final String EDGE_REMOVED_FROM_GRAPH =
      "Edge %s that was used to generate this set is no longer in the graph.";
  static final String REUSING_EDGE =
      "Edge %s already exists between the following nodes: %s, "
          + "so it cannot be reused to connect the following nodes: %s.";
  static final String MULTIPLE_EDGES_CONNECTING =
      "Cannot call edgeConnecting() when parallel edges exist between %s and %s. Consider calling "

  @Override
  public N removeInEdge(E edge, boolean isSelfLoop) {
    N node = super.removeInEdge(edge, isSelfLoop);
    Multiset<N> predecessors = getReference(predecessorsReference);
    if (predecessors != null) {
      checkState(predecessors.remove(node));
    }
    return node;
  }

  @Override
  public N removeOutEdge(E edge) {
    N node = super.removeOutEdge(edge);