}

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

      for (E incidentEdge : sanityCheckSet(network.incidentEdges(node))) {
        assertTrue(
            network.inEdges(node).contains(incidentEdge)

      }

      for (N successor : sanityCheckSet(graph.successors(node))) {
        allEndpointPairs.add(EndpointPair.of(graph, node, successor));
        assertThat(graph.predecessors(successor)).contains(node);
        assertThat(graph.hasEdgeConnecting(node, successor)).isTrue();
        assertThat(graph.incidentEdges(node)).contains(EndpointPair.of(graph, node, successor));
      }

    assume().that(graphIsMutable()).isTrue();

    addNode(N1);
    Set<Integer> successors = graph.successors(N1);
    assertThrows(UnsupportedOperationException.class, () -> successors.add(N2));
    putEdge(N1, N2);
    assertThat(graph.successors(N1)).containsExactlyElementsIn(successors);
  }

  @Override
  @Test
  public void incidentEdges_checkReturnedSetMutability() {

    assume().that(graphIsMutable()).isTrue();

    addNode(N1);
    Set<Integer> successors = network.successors(N1);
    assertThrows(UnsupportedOperationException.class, () -> successors.add(N2));
    addEdge(N1, N2, E12);
    assertThat(successors).containsExactlyElementsIn(network.successors(N1));
  }

  @Test
  public void edges_containsOrderMismatch() {
    addEdge(N1, N2, E12);

    assume().that(graphIsMutable()).isTrue();

    addNode(N1);
    Set<Integer> successors = network.successors(N1);
    assertThrows(UnsupportedOperationException.class, () -> successors.add(N2));
    addEdge(N1, N2, E12);
    assertThat(successors).containsExactlyElementsIn(network.successors(N1));
  }

  @Test
  public void edges_containsOrderMismatch() {
    addEdge(N1, N2, E12);

        checkArgument(incidentEdge.nodeU().equals(thisNode));

        N successor = incidentEdge.nodeV();
        V value = successorNodeToValueFn.apply(successor);

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

    assume().that(graphIsMutable()).isTrue();

    addNode(N1);
    Set<Integer> successors = graph.successors(N1);
    assertThrows(UnsupportedOperationException.class, () -> successors.add(N2));
    putEdge(N1, N2);
    assertThat(graph.successors(N1)).containsExactlyElementsIn(successors);
  }

  @Override
  @Test
  public void incidentEdges_checkReturnedSetMutability() {

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

  @Test
  public void edges_containsOrderMismatch() {
    addEdge(N1, N2, E12);

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

  @Test
  public void edges_containsOrderMismatch() {
    addEdge(N1, N2, E12);

      }

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

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

      // DO NOT override the AbstractGraph *degree() implementations.
    };
  }

  @Override
  public int degree(N node) {
    if (isDirected()) {