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

  @Test
  public void predecessors_oneEdge() {
    putEdge(N1, N2);

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

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

  @Test
  public void predecessors_oneEdge() {
    putEdge(N1, N2);

  public Set<E> adjacentEdges(E edge) {
    EndpointPair<N> endpointPair = incidentNodes(edge); // Verifies that edge is in this network.
    Set<E> endpointPairIncidentEdges =
        Sets.union(incidentEdges(endpointPair.nodeU()), incidentEdges(endpointPair.nodeV()));
    return edgeInvalidatableSet(
        Sets.difference(endpointPairIncidentEdges, ImmutableSet.of(edge)), edge);
  }

  @Override

    return nodeOrder;
  }

  @Override
  public ElementOrder<E> edgeOrder() {
    return edgeOrder;
  }

  @Override
  public Set<E> incidentEdges(N node) {
    return nodeInvalidatableSet(checkedConnections(node).incidentEdges(), node);
  }

  @Override
  public EndpointPair<N> incidentNodes(E edge) {
    N nodeU = checkedReferenceNode(edge);

   *         <li>{@code incidentEdges(node)}: Edge insertion order
   *       </ul>
   *   <li>For {@link Network}:
   *       <ul>
   *         <li>{@code adjacentNodes(node)}: Stable order
   *         <li>{@code predecessors(node)}: Connecting edge insertion order
   *         <li>{@code successors(node)}: Connecting edge insertion order
   *         <li>{@code incidentEdges(node)}: Stable order

  /**
   * Returns the count of {@code node}'s {@link #incidentEdges(Object) incident edges}, counting
   * 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}).

   */
  @Override
  Set<EndpointPair<N>> incidentEdges(N node);

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

 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 */
interface NetworkConnections<N, E> {

  Set<N> adjacentNodes();

  Set<N> predecessors();

  Set<N> successors();

  Set<E> incidentEdges();

  Set<E> inEdges();

  Set<E> outEdges();

  /**
   * Returns the set of edges connecting the origin node to {@code node}. For networks without

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

  @Override
  @Test
  public void adjacentNodes_checkReturnedSetMutability() {

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

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

  @Override
  @Test
  public void adjacentNodes_checkReturnedSetMutability() {