}

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

    addEdge(N1, N2, E12);
    Set<String> adjacentEdges = network.adjacentEdges(E12);
    try {
      adjacentEdges.add(E23);
      fail(ERROR_MODIFIABLE_COLLECTION);
    } catch (UnsupportedOperationException e) {

  }

  @Override
  public void adjacentEdges_checkReturnedSetMutability() {
    addEdge(N1, N2, E12);
    Set<String> adjacentEdges = network.adjacentEdges(E12);
    try {
      adjacentEdges.add(E23);
      fail(ERROR_MODIFIABLE_COLLECTION);
    } catch (UnsupportedOperationException e) {
      addEdge(N2, N3, E23);
      assertThat(network.adjacentEdges(E12)).containsExactlyElementsIn(adjacentEdges);
    }

  }

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

    addEdge(N1, N2, E12);
    Set<String> adjacentEdges = network.adjacentEdges(E12);
    try {
      adjacentEdges.add(E23);
      fail(ERROR_MODIFIABLE_COLLECTION);
    } catch (UnsupportedOperationException e) {

  }

  @Override
  public EndpointPair<N> incidentNodes(E edge) {
    return delegate().incidentNodes(edge);
  }

  @Override
  public Set<E> adjacentEdges(E edge) {
    return delegate().adjacentEdges(edge);
  }

  @Override
  public int degree(N node) {
    return delegate().degree(node);
  }

  @Override
  public int inDegree(N node) {

  }

  @Test
  public void adjacentEdges_edgeNotInGraph() {
    assertEdgeNotInGraphErrorMessage(
        assertThrows(
            IllegalArgumentException.class, () -> network.adjacentEdges(EDGE_NOT_IN_GRAPH)));
  }

  @Test
  public void adjacentEdges_parallelEdges() {
    assume().that(network.allowsParallelEdges()).isTrue();

    addEdge(N1, N2, E12);
    addEdge(N1, N2, E12_A);

  }

  @Test
  public void adjacentEdges_edgeNotInGraph() {
    assertEdgeNotInGraphErrorMessage(
        assertThrows(
            IllegalArgumentException.class, () -> network.adjacentEdges(EDGE_NOT_IN_GRAPH)));
  }

  @Test
  public void adjacentEdges_parallelEdges() {
    assume().that(network.allowsParallelEdges()).isTrue();

    addEdge(N1, N2, E12);
    addEdge(N1, N2, E12_A);

  }

  @Override
  public void adjacentEdges_checkReturnedSetMutability() {
    addEdge(N1, N2, E12);
    Set<String> adjacentEdges = network.adjacentEdges(E12);
    try {
      adjacentEdges.add(E23);
      fail(ERROR_MODIFIABLE_COLLECTION);
    } catch (UnsupportedOperationException e) {
      addEdge(N2, N3, E23);
      assertThat(network.adjacentEdges(E12)).containsExactlyElementsIn(adjacentEdges);
    }

    }

    @Override
    public EndpointPair<N> incidentNodes(E edge) {
      return network.incidentNodes(edge);
    }

    @Override
    public Set<E> adjacentEdges(E edge) {
      return network.adjacentEdges(edge);
    }

    // _don't_ override edge*Connecting*; we want the behavior from AbstractNetwork
  }

    }

    @Override
    public EndpointPair<N> incidentNodes(E edge) {
      return network.incidentNodes(edge);
    }

    @Override
    public Set<E> adjacentEdges(E edge) {
      return network.adjacentEdges(edge);
    }

    // _don't_ override edge*Connecting*; we want the behavior from AbstractNetwork
  }

   *         <li>{@code incidentEdges(node)}: Stable order
   *         <li>{@code inEdges(node)}: Edge insertion order
   *         <li>{@code outEdges(node)}: Edge insertion order
   *         <li>{@code adjacentEdges(edge)}: Stable order
   *         <li>{@code edgesConnecting(nodeU, nodeV)}: Edge insertion order
   *       </ul>
   * </ul>
   *
   * @since 29.0
   */
  public static <S> ElementOrder<S> stable() {