private static final Feature<?>[] COLLECTION_FEATURES = {
    CollectionSize.ANY, CollectionFeature.ALLOWS_NULL_QUERIES
  };

  private static final Feature<?>[] COLLECTION_FEATURES_ORDER = {
    CollectionSize.ANY, CollectionFeature.KNOWN_ORDER, CollectionFeature.ALLOWS_NULL_QUERIES
  };

  private static final Feature<?>[] COLLECTION_FEATURES_REMOVE = {

    assertEquals(Collections.singleton("a"), set);
  }

  public void testCopyOf_collection_oneElementRepeated() {
    Collection<String> c = MinimalCollection.of("a", "a", "a");
    Set<String> set = copyOf(c);
    assertEquals(Collections.singleton("a"), set);
  }

  public void testCopyOf_collection_general() {
    Collection<String> c = MinimalCollection.of("a", "b", "a");
    Set<String> set = copyOf(c);

    assertEquals(Collections.singleton("a"), set);
  }

  public void testCopyOf_collection_oneElementRepeated() {
    Collection<String> c = MinimalCollection.of("a", "a", "a");
    Set<String> set = copyOf(c);
    assertEquals(Collections.singleton("a"), set);
  }

  public void testCopyOf_collection_general() {
    Collection<String> c = MinimalCollection.of("a", "b", "a");
    Set<String> set = copyOf(c);

public class CollectionRetainAllTester<E> extends AbstractCollectionTester<E> {

  /** A collection of elements to retain, along with a description for use in failure messages. */
  private class Target {
    private final Collection<E> toRetain;
    private final String description;

    private Target(Collection<E> toRetain, String description) {
      this.toRetain = toRetain;
      this.description = description;
    }

   * </ol>
   *
   * @param collection the presumed-immutable collection
   * @param sampleElement an element of the same type as that contained by {@code collection}.
   *     {@code collection} may or may not have {@code sampleElement} as a member.
   */
  public static <E extends @Nullable Object> void assertCollectionIsUnmodifiable(
      Collection<E> collection, E sampleElement) {
    Collection<E> siblingCollection = new ArrayList<>();

    return Collections.emptySet();
  }

  protected Collection<Method> suppressForCheckedSet() {
    return Collections.emptySet();
  }

  protected Collection<Method> suppressForCheckedSortedSet() {
    return Collections.emptySet();
  }

  protected Collection<Method> suppressForAbstractSet() {
    return Collections.emptySet();
  }

  }

  private Collection<Method> suppressForEmptyNavigableMap() {
    return Collections.emptySet();
  }

  private Collection<Method> suppressForEmptySortedMap() {
    return Collections.emptySet();
  }

  protected Collection<Method> suppressForSingletonMap() {
    return Collections.emptySet();
  }

  protected Collection<Method> suppressForHashMap() {
    return Collections.emptySet();
  }

                  }

                  @Override
                  public SampleElements<Entry<String, Collection<String>>> samples() {
                    return new SampleElements<>(
                        Helpers.mapEntry("a", (Collection<String>) ImmutableSortedSet.of("alex")),
                        Helpers.mapEntry(

            projectKeys.add(key);
        }
        return projectKeys;
    }

    private Collection<String> negate(Collection<String> scopes) {
        Collection<String> result = new HashSet<>();
        Collections.addAll(result, "system", "compile", "provided", "runtime", "test");

        for (String scope : scopes) {
            if ("compile".equals(scope)) {
                result.remove("compile");

  }

  protected Collection<Method> suppressForHashMap() {
    return Collections.emptySet();
  }

  protected Collection<Method> suppressForHashtable() {
    return Collections.emptySet();
  }

  protected Collection<Method> suppressForLinkedHashMap() {
    return Collections.emptySet();
  }

  protected Collection<Method> suppressForTreeMapNatural() {
    return Collections.emptySet();
  }