@SuppressWarnings("SelfEquals")
  public void testEquals_self() {
    assertTrue("An Object should be equal to itself.", collection.equals(collection));
  }

  public void testEquals_null() {
    // noinspection ObjectEqualsNull
    assertFalse("An object should not be equal to null.", collection.equals(null));
  }

  public void testEquals_notACollection() {
    // noinspection EqualsBetweenInconvertibleTypes

    // setToTest should throw when it calls equals(), or equals is called on it, except for itself
    assertThat(setToTest).isEqualTo(setToTest);
    assertThrows(IllegalStateException.class, () -> setToTest.equals(wrappedSet));
    assertThrows(IllegalStateException.class, () -> setToTest.equals(copyOfWrappedSet));
    assertThrows(IllegalStateException.class, () -> setToTest.equals(copyOfModifiedSet));

    // setToTest should throw when it calls equals(), or equals is called on it, except for itself
    assertThat(setToTest).isEqualTo(setToTest);
    assertThrows(IllegalStateException.class, () -> setToTest.equals(wrappedSet));
    assertThrows(IllegalStateException.class, () -> setToTest.equals(copyOfWrappedSet));
    assertThrows(IllegalStateException.class, () -> setToTest.equals(copyOfModifiedSet));

    @Override
    public String toString() {
      assertTrue(Thread.holdsLock(mutex));
      return super.toString();
    }

    @Override
    public boolean equals(@Nullable Object o) {
      assertTrue(Thread.holdsLock(mutex));
      return super.equals(o);
    }

    @Override
    public int hashCode() {
      assertTrue(Thread.holdsLock(mutex));
      return super.hashCode();
    }

    @Override

    @SuppressWarnings("unchecked")
    K k = (K) t;
    int unused = comparator().compare(k, k);
    return t;
  }

  @Override
  public boolean equals(@Nullable Object obj) {
    return delegate.equals(obj);
  }

  @Override
  public int hashCode() {
    return delegate.hashCode();
  }

  @Override
  public String toString() {
    return delegate.toString();
  }

    @SuppressWarnings("unchecked")
    K k = (K) t;
    int unused = comparator().compare(k, k);
    return t;
  }

  @Override
  public boolean equals(@Nullable Object obj) {
    return delegate.equals(obj);
  }

  @Override
  public int hashCode() {
    return delegate.hashCode();
  }

  @Override
  public String toString() {
    return delegate.toString();
  }

    assertTrue(
        "multiset doesn't equal a multiset with the same elements",
        getMultiset().equals(HashMultiset.create(getSampleElements())));
  }

  public void testEquals_differentSize() {
    Multiset<E> other = HashMultiset.create(getSampleElements());
    other.add(e0());
    assertFalse("multiset equals a multiset with a different size", getMultiset().equals(other));
  }

  public <T extends @Nullable Object> T[] toArray(T[] other) {
    return delegate.toArray(other);
  }

  @Override
  public String toString() {
    return delegate.toString();
  }

  // TODO(cpovirk): equals(), as well, in case it's any faster than Sets.equalsImpl?

  @Override
  public int hashCode() {
    return delegate.hashCode();
  }

    this.element = Preconditions.checkNotNull(element);
  }

  @Override
  public int size() {
    return 1;
  }

  @Override
  public boolean contains(@CheckForNull Object target) {
    return element.equals(target);
  }

  @Override
  public UnmodifiableIterator<E> iterator() {
    return Iterators.singletonIterator(element);
  }

  @Override
  public ImmutableList<E> asList() {

  /** Constructor for use by subclasses. */
  protected ForwardingSet() {}

  @Override
  protected abstract Set<E> delegate();

  @Override
  public boolean equals(@CheckForNull Object object) {
    return object == this || delegate().equals(object);
  }

  @Override
  public int hashCode() {
    return delegate().hashCode();
  }

  /**