}

  @Test
  public void edges_containsOrderMismatch() {
    addEdge(N1, N2, E12);
    EndpointPair<Integer> endpointsN1N2 = EndpointPair.unordered(N1, N2);
    EndpointPair<Integer> endpointsN2N1 = EndpointPair.unordered(N2, N1);
    assertThat(network.asGraph().edges()).doesNotContain(endpointsN1N2);
    assertThat(network.asGraph().edges()).doesNotContain(endpointsN2N1);
  }

  @Test

 */
abstract class AbstractGraphBuilder<N> {
  final boolean directed;
  boolean allowsSelfLoops = false;
  ElementOrder<N> nodeOrder = ElementOrder.insertion();
  ElementOrder<N> incidentEdgeOrder = ElementOrder.unordered();

  @Nullable Integer expectedNodeCount = null;

  /**
   * Creates a new instance with the specified edge directionality.
   *

  @Parameters(name = "allowsSelfLoops={0}, incidentEdgeOrder={1}")
  public static Collection<Object[]> parameters() {
    return Arrays.asList(
        new Object[][] {
          {false, ElementOrder.unordered()},
          {true, ElementOrder.unordered()},
          {false, ElementOrder.stable()},
          {true, ElementOrder.stable()},
        });
  }

  private final boolean allowsSelfLoops;

  @Parameters(name = "allowsSelfLoops={0}, incidentEdgeOrder={1}")
  public static Collection<Object[]> parameters() {
    return Arrays.asList(
        new Object[][] {
          {false, ElementOrder.unordered()},
          {true, ElementOrder.unordered()},
          {false, ElementOrder.stable()},
          {true, ElementOrder.stable()},
        });
  }

  private final boolean allowsSelfLoops;

      Collector.of(
          () -> new ToOptionalState<>(null),
          ToOptionalState::add,
          ToOptionalState::combine,
          ToOptionalState::getOptional,
          Collector.Characteristics.UNORDERED);

  /**
   * A collector that converts a stream of zero or one elements to an {@code Optional}.
   *
   * @throws IllegalArgumentException if the stream consists of two or more elements.

      Collector.of(
          () -> new ToOptionalState<>(null),
          ToOptionalState::add,
          ToOptionalState::combine,
          ToOptionalState::getOptional,
          Collector.Characteristics.UNORDERED);

  /**
   * A collector that converts a stream of zero or one elements to an {@code Optional}.
   *
   * @throws IllegalArgumentException if the stream consists of two or more elements.

    void checkAcquiredLock(Policy policy, LockGraphNode acquiredLock) {
      // checkAcquiredLock() should never be invoked by a lock that has already
      // been acquired. For unordered locks, aboutToAcquire() ensures this by
      // checking isAcquiredByCurrentThread(). For ordered locks, however, this
      // can happen because multiple locks may share the same LockGraphNode. In
      // this situation, throw an IllegalStateException as defined by contract

    List<T> list = Arrays.asList(inputs);
    doExpectCollects(expectedResult, list);
    if (collector.characteristics().contains(Collector.Characteristics.UNORDERED)) {
      Collections.reverse(list);
      doExpectCollects(expectedResult, list);
    }
    return this;
  }

  private void doExpectCollects(R expectedResult, List<T> inputs) {

    List<T> list = Arrays.asList(inputs);
    doExpectCollects(expectedResult, list);
    if (collector.characteristics().contains(Collector.Characteristics.UNORDERED)) {
      Collections.reverse(list);
      doExpectCollects(expectedResult, list);
    }
    return this;
  }

  private void doExpectCollects(R expectedResult, List<T> inputs) {

    return Collector.of(
        () -> TopKSelector.<T>least(k, comparator),
        TopKSelector::offer,
        TopKSelector::combine,
        TopKSelector::topK,
        Collector.Characteristics.UNORDERED);
  }

  /**
   * Returns a {@code Collector} that returns the {@code k} greatest (relative to the specified
   * {@code Comparator}) input elements, in descending order, as an unmodifiable {@code List}. Ties