Iterator<Integer> iter = Iterators.forEnumeration(enumer);

    assertFalse(iter.hasNext());
    assertThrows(NoSuchElementException.class, () -> iter.next());
  }

  @SuppressWarnings("DoNotCall")
  public void testForEnumerationSingleton() {
    Enumeration<Integer> enumer = enumerate(1);
    Iterator<Integer> iter = Iterators.forEnumeration(enumer);

    assertTrue(iter.hasNext());

    Iterator<Integer> iter = Iterators.forEnumeration(enumer);

    assertFalse(iter.hasNext());
    assertThrows(NoSuchElementException.class, () -> iter.next());
  }

  @SuppressWarnings("DoNotCall")
  public void testForEnumerationSingleton() {
    Enumeration<Integer> enumer = enumerate(1);
    Iterator<Integer> iter = Iterators.forEnumeration(enumer);

    assertTrue(iter.hasNext());

   * return an {@code UnmodifiableIterator} instead of a plain {@code Iterator}.
   */
  public static <T extends @Nullable Object> UnmodifiableIterator<T> forEnumeration(
      Enumeration<T> enumeration) {
    checkNotNull(enumeration);
    return new UnmodifiableIterator<T>() {
      @Override
      public boolean hasNext() {
        return enumeration.hasMoreElements();