* doing so would be to derive a separate test library by using remove_from_jar to strip out
   * ClassValueValidator.
   *
   * Fortunately, we get pretty good coverage "by accident": We run all these tests against the
   * *backport*, where ClassValueValidator is not present.
   */

   * self-loops twice (equivalently, the number of times an edge touches {@code node}).
   *
   * <p>For directed networks, this is equal to {@code inDegree(node) + outDegree(node)}.
   *
   * <p>For undirected networks, this is equal to {@code incidentEdges(node).size()} + (number of
   * self-loops incident to {@code node}).
   *

    directedGraph.putEdge(N1, N2);
    directedGraph.putEdge(N2, N1);
    directedGraph.putEdge(N1, N3); // only incident to one node in nodeSubset
    directedGraph.putEdge(N4, N4);
    directedGraph.putEdge(5, 6); // not incident to any node in nodeSubset

    MutableGraph<Integer> expectedSubgraph = GraphBuilder.directed().allowsSelfLoops(true).build();
    expectedSubgraph.putEdge(N1, N2);

    assertThat(network.allowsSelfLoops()).isEqualTo(asGraph.allowsSelfLoops());

    for (E edge : sanityCheckSet(network.edges())) {
      // TODO(b/27817069): Consider verifying the edge's incident nodes in the string.
      assertThat(edgeString).contains(edge.toString());

      EndpointPair<N> endpointPair = network.incidentNodes(edge);
      N nodeU = endpointPair.nodeU();
      N nodeV = endpointPair.nodeV();

        // If the implementation uses identityHashCode(), referential equality is
        // probably intended. So no point in using an equal-but-different factory argument.
        // We check twice to avoid confusion caused by accidental hash collision.
        equalArgs.set(i, shouldBeEqualArg);
      }
    }
    return equalArgs;
  }

  private static boolean hashCodeInsensitiveToArgReference(

   * that contains all of the nodes in {@code nodes}, and all of the {@link Network#edges() edges}
   * from {@code network} for which the {@link Network#incidentNodes(Object) incident nodes} are
   * both contained by {@code nodes}.
   *
   * @throws IllegalArgumentException if any element in {@code nodes} is not a node in the graph
   */
  public static <N, E> MutableNetwork<N, E> inducedSubgraph(

   * that contains all of the nodes in {@code nodes}, and all of the {@link Network#edges() edges}
   * from {@code network} for which the {@link Network#incidentNodes(Object) incident nodes} are
   * both contained by {@code nodes}.
   *
   * @throws IllegalArgumentException if any element in {@code nodes} is not a node in the graph
   */
  public static <N, E> MutableNetwork<N, E> inducedSubgraph(

        // If the implementation uses identityHashCode(), referential equality is
        // probably intended. So no point in using an equal-but-different factory argument.
        // We check twice to avoid confusion caused by accidental hash collision.
        equalArgs.set(i, shouldBeEqualArg);
      }
    }
    return equalArgs;
  }

  private static boolean hashCodeInsensitiveToArgReference(