}

  @Test
  public void predecessors_noPredecessors() {
    addNode(N1);
    assertThat(graph.predecessors(N1)).isEmpty();
  }

  @Test
  public void predecessors_nodeNotInGraph() {
    assertNodeNotInGraphErrorMessage(
        assertThrows(IllegalArgumentException.class, () -> graph.predecessors(NODE_NOT_IN_GRAPH)));
  }

  @Test

  }

  @Test
  public void predecessors_noPredecessors() {
    addNode(N1);
    assertThat(graph.predecessors(N1)).isEmpty();
  }

  @Test
  public void predecessors_nodeNotInGraph() {
    assertNodeNotInGraphErrorMessage(
        assertThrows(IllegalArgumentException.class, () -> graph.predecessors(NODE_NOT_IN_GRAPH)));
  }

  @Test

  }

  @Override
  @Test
  public void predecessors_checkReturnedSetMutability() {
    assume().that(graphIsMutable()).isTrue();

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

  }

  @Override
  @Test
  public void predecessors_checkReturnedSetMutability() {
    assume().that(graphIsMutable()).isTrue();

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

  }

  @Test
  public void predecessors_noPredecessors() {
    addNode(N1);
    assertThat(network.predecessors(N1)).isEmpty();
  }

  @Test
  public void predecessors_nodeNotInGraph() {
    assertNodeNotInGraphErrorMessage(
        assertThrows(
            IllegalArgumentException.class, () -> network.predecessors(NODE_NOT_IN_GRAPH)));
  }

  @Test

  }

  @Test
  public void predecessors_noPredecessors() {
    addNode(N1);
    assertThat(network.predecessors(N1)).isEmpty();
  }

  @Test
  public void predecessors_nodeNotInGraph() {
    assertNodeNotInGraphErrorMessage(
        assertThrows(
            IllegalArgumentException.class, () -> network.predecessors(NODE_NOT_IN_GRAPH)));
  }

  @Test

  }

  @Override
  @Test
  public void predecessors_checkReturnedSetMutability() {
    assume().that(graphIsMutable()).isTrue();

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

  /** Remove {@code node} from the set of predecessors. */
  void removePredecessor(N node);

  /**
   * Remove {@code node} from the set of successors. Returns the value previously associated with
   * the edge connecting the two nodes.
   */
  @CanIgnoreReturnValue
  @CheckForNull
  V removeSuccessor(N node);

  /**
   * Add {@code node} as a predecessor to the origin node. In the case of an undirected graph, it

  @Override
  public Set<N> predecessors() {
    return Collections.unmodifiableSet(predecessorsMultiset().elementSet());
  }

  private Multiset<N> predecessorsMultiset() {
    Multiset<N> predecessors = getReference(predecessorsReference);
    if (predecessors == null) {
      predecessors = HashMultiset.create(inEdgeMap.values());

  }

  private static final int ENDPOINT = -2;

  // TODO(user): predecessors and successors should be collocated (reducing cache misses).
  // Might also explore collocating all of [hash, next, predecessor, successor] fields of an
  // entry in a *single* long[], though that reduces the maximum size of the set by a factor of 2

  /**
   * Pointer to the predecessor of an entry in insertion order. ENDPOINT indicates a node is the