}
        assertThat(
                graph.predecessors(node).contains(adjacentNode)
                    || graph.successors(node).contains(adjacentNode))
            .isTrue();
      }

      for (N predecessor : sanityCheckSet(graph.predecessors(node))) {
        assertThat(graph.successors(predecessor)).contains(node);
        assertThat(graph.hasEdgeConnecting(predecessor, node)).isTrue();

        }
        assertThat(
                graph.predecessors(node).contains(adjacentNode)
                    || graph.successors(node).contains(adjacentNode))
            .isTrue();
      }

      for (N predecessor : sanityCheckSet(graph.predecessors(node))) {
        assertThat(graph.successors(predecessor)).contains(node);
        assertThat(graph.hasEdgeConnecting(predecessor, node)).isTrue();

                      Iterators.transform(
                          graph.predecessors(node).iterator(),
                          (N predecessor) -> EndpointPair.ordered(predecessor, node)),
                      Iterators.transform(
                          // filter out 'node' from successors (already covered by predecessors,
                          // above)

        N predecessor = incidentEdge.nodeU();

        Object existingValue = adjacentNodeValues.put(predecessor, PRED);
        if (existingValue != null) {
          adjacentNodeValues.put(predecessor, new PredAndSucc(existingValue));
        }

        orderedNodeConnectionsBuilder.add(new NodeConnection.Pred<>(predecessor));
        predecessorCount++;

                        Object key = getPluginKey(element);

                        master.put(key, plugin);
                    }
                }

                Map<Object, List<Plugin>> predecessors = new LinkedHashMap<>();
                List<Plugin> pending = new ArrayList<>();
                for (Plugin element : tgt) {
                    Object key = getPluginKey(element);

  @Test
  public void predecessors_checkReturnedSetMutability() {
    addNode(N2);
    Set<Integer> predecessors = network.predecessors(N2);
    assertThrows(UnsupportedOperationException.class, () -> predecessors.add(N1));
    addEdge(N1, N2, E12);
    assertThat(network.predecessors(N2)).containsExactlyElementsIn(predecessors);
  }

  @Override
  @Test
  public void successors_checkReturnedSetMutability() {

  @Override
  ElementOrder<N> nodeOrder();

  /**
   * Returns an {@link ElementOrder} that specifies the order of iteration for the elements of
   * {@link #edges()}, {@link #adjacentNodes(Object)}, {@link #predecessors(Object)}, {@link
   * #successors(Object)} and {@link #incidentEdges(Object)}.
   *
   * @since 29.0
   */
  @Override
  ElementOrder<N> incidentEdgeOrder();

  //
  // Element-level accessors

  @Override
  ElementOrder<N> nodeOrder();

  /**
   * Returns an {@link ElementOrder} that specifies the order of iteration for the elements of
   * {@link #edges()}, {@link #adjacentNodes(Object)}, {@link #predecessors(Object)}, {@link
   * #successors(Object)} and {@link #incidentEdges(Object)}.
   *
   * @since 29.0
   */
  @Override
  ElementOrder<N> incidentEdgeOrder();

  //
  // Element-level accessors

  @Override
  ElementOrder<N> nodeOrder();

  /**
   * Returns an {@link ElementOrder} that specifies the order of iteration for the elements of
   * {@link #edges()}, {@link #adjacentNodes(Object)}, {@link #predecessors(Object)}, {@link
   * #successors(Object)} and {@link #incidentEdges(Object)}.
   *
   * @since 29.0
   */
  @Override
  ElementOrder<N> incidentEdgeOrder();

  //
  // Element-level accessors

      }

      @Override
      public Set<N> adjacentNodes(N node) {
        return AbstractNetwork.this.adjacentNodes(node);
      }

      @Override
      public Set<N> predecessors(N node) {
        return AbstractNetwork.this.predecessors(node);
      }

      @Override
      public Set<N> successors(N node) {
        return AbstractNetwork.this.successors(node);
      }