}

  // Node/edge sets are the same, but node/edge connections differ due to edge type.
  @Test
  public void equivalent_directedVsUndirected() {
    graph.putEdge(N1, N2);

    MutableGraph<Integer> g2 = createGraph(oppositeType(edgeType));
    g2.putEdge(N1, N2);

    assertThat(graph).isNotEqualTo(g2);
  }

  // Node/edge sets and node/edge connections are the same, but directedness differs.

  }

  // Node/edge sets are the same, but node/edge connections differ due to edge type.
  @Test
  public void equivalent_directedVsUndirected() {
    graph.putEdge(N1, N2);

    MutableGraph<Integer> g2 = createGraph(oppositeType(edgeType));
    g2.putEdge(N1, N2);

    assertThat(graph).isNotEqualTo(g2);
  }

  // Node/edge sets and node/edge connections are the same, but directedness differs.

      }
    };
  }

  @Override
  public @Nullable N removeInEdge(E edge, boolean isSelfLoop) {
    if (!isSelfLoop) {
      return removeOutEdge(edge);
    }
    return null;
  }

  @Override
  public N removeOutEdge(E edge) {
    N node = super.removeOutEdge(edge);
    Multiset<N> adjacentNodes = getReference(adjacentNodesReference);
    if (adjacentNodes != null) {

   *
   * @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);

  /**

  }

  @Override
  public N adjacentNode(E edge) {
    // Since the reference node is defined to be 'source' for directed graphs,
    // we can assume this edge lives in the set of outgoing edges.
    // (We're relying on callers to call this method only with an edge that's in the graph.)
    return requireNonNull(outEdgeMap.get(edge));
  }

  @Override
  public N removeInEdge(E edge, boolean isSelfLoop) {
    if (isSelfLoop) {

    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) {

      Collections.shuffle(edgeList, gen);
      int numEdgesToRemove = gen.nextInt(NUM_EDGES);
      for (int i = 0; i < numEdgesToRemove; ++i) {
        EndpointPair<Integer> edge = edgeList.get(i);
        assertThat(graph.removeEdge(edge.nodeU(), edge.nodeV())).isTrue();
      }

      assertThat(graph.nodes()).hasSize(NUM_NODES);
      assertThat(graph.edges()).hasSize(NUM_EDGES - numEdgesToRemove);

  /**
   * Returns the nodes which are the endpoints of {@code edge} in this network.
   *
   * @throws IllegalArgumentException if {@code edge} is not an element of this network
   */
  EndpointPair<N> incidentNodes(E edge);

  /**
   * Returns a live view of the edges which have an {@link #incidentNodes(Object) incident node} in
   * common with {@code edge}. An edge is not considered adjacent to itself.
   *

/**
 * An immutable pair representing the two endpoints of an edge in a graph. The {@link EndpointPair}
 * of a directed edge is an ordered pair of nodes ({@link #source()} and {@link #target()}). The
 * {@link EndpointPair} of an undirected edge is an unordered pair of nodes ({@link #nodeU()} and
 * {@link #nodeV()}).
 *
 * <p>The edge is a self-loop if, and only if, the two endpoints are equal.
 *
 * @author James Sexton

      assertThat(network.inEdges(nodeV)).contains(edge);
      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));
        }
      }