public abstract class ImmutableSet<E> extends ImmutableCollection<E> implements Set<E> {
  ImmutableSet() {}

  public static <E> Collector<E, ?, ImmutableSet<E>> toImmutableSet() {
    return CollectCollectors.toImmutableSet();
  }

  // Casting to any type is safe because the set will never hold any elements.
  @SuppressWarnings({"unchecked"})
  public static <E> ImmutableSet<E> of() {

    if (result == null) {
      return inverse = new SingletonImmutableBiMap<V, K>(singleValue, singleKey, this);
    } else {
      return result;
    }
  }

  @Override
  public ImmutableSet<V> values() {
    return ImmutableSet.of(singleValue);
  }

  private static final QuantilesAlgorithm REFERENCE_ALGORITHM = QuantilesAlgorithm.SORTING;
  private static final ImmutableSet<QuantilesAlgorithm> NON_REFERENCE_ALGORITHMS =
      Sets.difference(
              ImmutableSet.copyOf(QuantilesAlgorithm.values()),
              ImmutableSet.of(REFERENCE_ALGORITHM))
          .immutableCopy();

  private double[] dataset;

  @Override
  protected void setUp() {

          return key.toString();
        }
      };

  private CacheBuilderFactory factoryWithAllKeyStrengths() {
    return new CacheBuilderFactory()
        .withKeyStrengths(ImmutableSet.of(STRONG, Strength.WEAK))
        .withValueStrengths(ImmutableSet.of(STRONG, Strength.WEAK, Strength.SOFT));
  }

  private Iterable<LoadingCache<Key, String>> caches() {
    CacheBuilderFactory factory = factoryWithAllKeyStrengths();

      return new SampleElements<>(
          mapEntry("one", ImmutableSet.of(10000)),
          mapEntry("two", ImmutableSet.of(-2000)),
          mapEntry("three", ImmutableSet.of(300)),
          mapEntry("four", ImmutableSet.of(-40)),
          mapEntry("five", ImmutableSet.of(5)));
    }

    @Override
    public Map<String, Collection<Integer>> create(Object... elements) {

    // invalidate setToTest
    wrappedSet.remove(1);
    // sanity check on update of wrappedSet
    assertThat(wrappedSet).isNotEqualTo(copyOfWrappedSet);

    ImmutableSet<Integer> copyOfModifiedSet = ImmutableSet.copyOf(wrappedSet); // {2,3}
    // sanity check on construction of copyOfModifiedSet
    assertThat(wrappedSet).isEqualTo(copyOfModifiedSet);

  }

  @Override
  public @Nullable V get(@Nullable Object key) {
    return (key == null) ? null : Maps.safeGet(delegate, key);
  }

  @Override
  ImmutableSet<Entry<K, V>> createEntrySet() {
    return ImmutableSet.unsafeDelegate(
        new ForwardingSet<Entry<K, V>>() {
          @Override
          protected Set<Entry<K, V>> delegate() {
            return delegate.entrySet();
          }

  }

  @Override
  boolean isPartialView() {
    return false;
  }

  @Override
  ImmutableSet<Entry<K, V>> createEntrySet() {
    return ImmutableSet.of(immutableEntry(singleKey, singleValue));
  }

  @Override
  ImmutableSet<K> createKeySet() {
    return ImmutableSet.of(singleKey);
  }

  private final transient @Nullable ImmutableBiMap<V, K> inverse;

  private final byte[] bytes;
  private final ImmutableSet<TestOption> options;

  private boolean inputStreamOpened;
  private boolean inputStreamClosed;

  TestByteSource(byte[] bytes, TestOption... options) {
    this.bytes = checkNotNull(bytes);
    this.options = ImmutableSet.copyOf(options);
  }

  @Override
  public boolean wasStreamOpened() {

  private final byte[] bytes;
  private final ImmutableSet<TestOption> options;

  private boolean inputStreamOpened;
  private boolean inputStreamClosed;

  TestByteSource(byte[] bytes, TestOption... options) {
    this.bytes = checkNotNull(bytes);
    this.options = ImmutableSet.copyOf(options);
  }

  @Override
  public boolean wasStreamOpened() {