}

      for (N predecessor : sanityCheckSet(network.predecessors(node))) {
        assertThat(network.successors(predecessor)).contains(node);
        assertThat(network.edgesConnecting(predecessor, node)).isNotEmpty();
      }

      for (N successor : sanityCheckSet(network.successors(node))) {
        assertThat(network.predecessors(successor)).contains(node);

   * contains(). Verify that these sets are consistent with the elements of their iterator.
   */
  @CanIgnoreReturnValue
  static <T> Set<T> sanityCheckSet(Set<T> set) {
    assertThat(set).hasSize(Iterators.size(set.iterator()));
    for (Object element : set) {
      assertThat(set).contains(element);
    }
    assertThat(set).doesNotContain(new Object());