}

  public void testEmpty_comparator() {
    SortedSet<String> set = of();
    assertSame(Ordering.natural(), set.comparator());
  }

  public void testEmpty_headSet() {
    SortedSet<String> set = of();
    assertSame(set, set.headSet("c"));
  }

  public void testEmpty_tailSet() {
    SortedSet<String> set = of();
    assertSame(set, set.tailSet("f"));
  }

  public void testEmpty_subSet() {

                  @Override
                  protected Set<String> create(String[] elements) {
                    Set<String> set = Sets.newHashSet("b", "c");
                    Set<String> other = Sets.newHashSet("a", "b", "c", "d");
                    return Sets.difference(set, other);
                  }
                })
            .named("set - superset")
            .withFeatures(

        initialValue,
        getList().set(index, newValue));
    assertEquals("After set(i, x), get(i) should return x", newValue, getList().get(index));
    assertEquals("set() should not change the size of a list.", getNumElements(), getList().size());
  }

  @ListFeature.Require(SUPPORTS_SET)
  public void testSet_indexTooLow() {
    try {
      getList().set(-1, e3());

      }
    }
    return features;
  }

  /**
   * Given a set of features, return a new set of all features directly or indirectly implied by any
   * of them.
   *
   * @param features the set of features whose implications to find
   * @return the implied set of features
   */
  public static Set<Feature<?>> impliedFeatures(Set<Feature<?>> features) {
    Set<Feature<?>> impliedSet = new LinkedHashSet<>();

    assertTrue(
        "A Set should equal any other Set containing the same elements,"
            + " even if some elements are null.",
        getSet().equals(MinimalSet.from(elements)));
  }

  @CollectionSize.Require(absent = CollectionSize.ZERO)
  public void testEquals_otherContainsNull() {
    Collection<E> elements = getSampleElements(getNumElements() - 1);
    elements.add(null);
    Set<E> other = MinimalSet.from(elements);

  }

  public void testFrequency_set() {
    Set<String> set = Sets.newHashSet("a", "b", "c");
    assertEquals(1, Iterables.frequency(set, "a"));
    assertEquals(1, Iterables.frequency(set, "b"));
    assertEquals(1, Iterables.frequency(set, "c"));
    assertEquals(0, Iterables.frequency(set, "d"));
    assertEquals(0, Iterables.frequency(set, 4.2));
    assertEquals(0, Iterables.frequency(set, null));
  }

import java.util.Set;

/**
 * Optional features of classes derived from {@code Set}.
 *
 * @author George van den Driessche
 */
@SuppressWarnings("rawtypes") // maybe avoidable if we rework the whole package?
@GwtCompatible
public enum SetFeature implements Feature<Set> {
  GENERAL_PURPOSE(CollectionFeature.GENERAL_PURPOSE);

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

      }
    }
    Collections.shuffle(queryList, random);
    return queryList.toArray(new Element[0]);
  }

  private Set<Element> createData() {
    Set<Element> set = Sets.newHashSetWithExpectedSize(size);
    while (set.size() < size) {
      set.add(newElement());
    }
    return set;
  }

  private Element newElement() {
    int value = random.nextInt();

   *
   * @param collection the elements that the set should contain
   * @return a new {@code CompactLinkedHashSet} containing those elements (minus duplicates)
   */
  public static <E extends @Nullable Object> CompactLinkedHashSet<E> create(
      Collection<? extends E> collection) {
    CompactLinkedHashSet<E> set = createWithExpectedSize(collection.size());
    set.addAll(collection);
    return set;
  }

  /**

              @Override
              protected Set<String> create(String[] elements) {
                TestSet<String> inner = new TestSet<>(new HashSet<String>(), MUTEX);
                Set<String> outer = Synchronized.set(inner, inner.mutex);
                Collections.addAll(outer, elements);
                return outer;
              }
            })
        .named("Synchronized.set")
        .withFeatures(