* @author George van den Driessche
 */
@GwtCompatible
public interface Feature<T> {
  /** Returns the set of features that are implied by this feature. */
  Set<Feature<? super T>> getImpliedFeatures();

    // gives a predictable order of test suites.
    this.implied = copyToSet(implied);
    this.numElements = null;
  }

  @Override
  public Set<Feature<? super Collection>> getImpliedFeatures() {
    return implied;
  }

  public int getNumElements() {
    if (numElements == null) {
      throw new IllegalStateException(
          "A compound CollectionSize doesn't specify a number of elements.");

  private final Set<Feature<? super List>> implied;

  ListFeature(Feature<? super List>... implied) {
    this.implied = copyToSet(implied);
  }

  @Override
  public Set<Feature<? super List>> getImpliedFeatures() {
    return implied;
  }

  @Retention(RetentionPolicy.RUNTIME)
  @Inherited
  @TesterAnnotation
  public @interface Require {
    ListFeature[] value() default {};

  /**
   * Indicates that elements from {@code Multiset.entrySet()} update to reflect changes in the
   * backing multiset.
   */
  ENTRIES_ARE_VIEWS;

  @Override
  public Set<Feature<? super Multiset>> getImpliedFeatures() {
    return emptySet();
  }

  @Retention(RetentionPolicy.RUNTIME)
  @Inherited
  @TesterAnnotation
  public @interface Require {
    public abstract MultisetFeature[] value() default {};

   * created for them.
   */
  enum NoRecurse implements Feature<@Nullable Void> {
    SUBMAP,
    DESCENDING;

    @Override
    public Set<Feature<? super @Nullable Void>> getImpliedFeatures() {
      return emptySet();
    }
  }

  /**
   * Creates a suite whose map has some elements filtered out of view.
   *

    testers.add(BiMapClearTester.class);
    return testers;
  }

  enum NoRecurse implements Feature<Void> {
    INVERSE;

    @Override
    public Set<Feature<? super Void>> getImpliedFeatures() {
      return emptySet();
    }
  }

  @Override
  protected List<TestSuite> createDerivedSuites(
      FeatureSpecificTestSuiteBuilder<

  CollectionFeature(Feature<? super Collection>... implied) {
    this.implied = copyToSet(implied);
  }

  @Override
  public Set<Feature<? super Collection>> getImpliedFeatures() {
    return implied;
  }

  @Retention(RetentionPolicy.RUNTIME)
  @Inherited
  @TesterAnnotation
  public @interface Require {
    CollectionFeature[] value() default {};

   * created for them.
   */
  enum NoRecurse implements Feature<@Nullable Void> {
    SUBMAP,
    DESCENDING;

    @Override
    public Set<Feature<? super @Nullable Void>> getImpliedFeatures() {
      return emptySet();
    }
  }

  /**
   * Creates a suite whose map has some elements filtered out of view.
   *

    return new MultisetTestSuiteBuilder<E>().usingGenerator(generator);
  }

  public enum NoRecurse implements Feature<Void> {
    NO_ENTRY_SET;

    @Override
    public Set<Feature<? super Void>> getImpliedFeatures() {
      return emptySet();
    }
  }

  @SuppressWarnings("rawtypes") // class literals
  @Override
  protected List<Class<? extends AbstractTester>> getTesters() {

    FOO,
    IMPLIES_FOO,
    IMPLIES_IMPLIES_FOO,
    BAR,
    IMPLIES_BAR,
    IMPLIES_IMPLIES_FOO_AND_IMPLIES_BAR;

    @Override
    public ImmutableSet<Feature<? super Object>> getImpliedFeatures() {
      switch (this) {
        case IMPLIES_FOO:
          return ImmutableSet.of(FOO);
        case IMPLIES_IMPLIES_FOO:
          return ImmutableSet.of(IMPLIES_FOO);
        case IMPLIES_BAR: