public final class ForwardingWrapperTester {

  private boolean testsEquals = false;

  /**
   * Asks for {@link Object#equals} and {@link Object#hashCode} to be tested. That is, forwarding
   * wrappers of equal instances should be equal.
   */
  @CanIgnoreReturnValue
  public ForwardingWrapperTester includingEquals() {
    this.testsEquals = true;
    return this;
  }

  /**

   * throws an {@link IllegalArgumentException} when presented with duplicate elements instead of
   * collapsing them to a single element or including duplicate instances in the collection.
   */
  REJECTS_DUPLICATES_AT_CREATION,

  SUPPORTS_ADD,
  SUPPORTS_REMOVE,
  SUPPORTS_ITERATOR_REMOVE,
  FAILS_FAST_ON_CONCURRENT_MODIFICATION,

  /**

 * used; or if the class exposes a public parameter-less constructor then it will be "new"d and
 * returned.
 *
 * <p>All default instances returned by {@link #get} are generics-safe. Clients won't get type
 * errors for using {@code get(Comparator.class)} as a {@code Comparator<Foo>}, for example.
 * Immutable empty instances are returned for collection types; {@code ""} for string; {@code 0} for

   * features to support (from the enclosing {@link AbstractIteratorTester} instance). Instead of
   * throwing exceptions like {@link NoSuchElementException} at the appropriate times, it throws
   * {@link PermittedMetaException} instances, which wrap a set of all exceptions that the iterator
   * could throw during the invocation of that method. This is necessary because, e.g., a call to
   * {@code iterator().remove()} of an unmodifiable list could throw either {@link

   * }</pre>
   *
   * <p>As a workaround, it is always safe to cast an {@code Optional<? extends T>} to {@code
   * Optional<T>}. Casting either of the above example {@code Optional} instances to {@code
   * Optional<Number>} (where {@code Number} is the desired output type) solves the problem:
   *
   * <pre>{@code
   * Optional<Number> optionalInt = (Optional) getSomeOptionalInt();

  public void testAddNullReference() {
    assertThrows(NullPointerException.class, () -> equalsTester.addEqualityGroup((Object) null));
  }

  /** Test equalObjects after adding multiple instances at once with a null */
  public void testAddTwoEqualObjectsAtOnceWithNull() {
    assertThrows(
        NullPointerException.class,
        () -> equalsTester.addEqualityGroup(reference, equalObject1, null));
  }

   * building, it is still possible to change the options used to build the ThreadFactory and/or
   * build again. State is not shared amongst built instances.
   *
   * @return the fully constructed {@link ThreadFactory}
   */
  public ThreadFactory build() {
    return doBuild(this);
  }

 * {@code CharSink} is not an open, stateful stream that can be written to and closed. Instead, it
 * is an immutable <i>supplier</i> of {@code Writer} instances.
 *
 * <p>{@code CharSink} provides two kinds of methods:
 *
 * <ul>
 *   <li><b>Methods that return a writer:</b> These methods should return a <i>new</i>, independent

    return Arrays.copyOf(empty, length);
  }

  /** Equivalent to Arrays.copyOfRange(source, from, to, arrayOfType.getClass()). */
  /*
   * Arrays are a mess from a nullness perspective, and Class instances for object-array types are
   * even worse. For now, we just suppress and move on with our lives.
   *
   * - https://github.com/jspecify/jspecify/issues/65
   *

    return Arrays.copyOf(empty, length);
  }

  /** Equivalent to Arrays.copyOfRange(source, from, to, arrayOfType.getClass()). */
  /*
   * Arrays are a mess from a nullness perspective, and Class instances for object-array types are
   * even worse. For now, we just suppress and move on with our lives.
   *
   * - https://github.com/jspecify/jspecify/issues/65
   *