assertIteratorIsUnmodifiable(COMMA_SPLITTER.split("a,b").iterator());
  }

  public void testSplitterIterableIsUnmodifiable_string() {
    assertIteratorIsUnmodifiable(Splitter.on(",").split("a,b").iterator());
  }

  @GwtIncompatible // java.util.regex.Pattern
  public void testSplitterIterableIsUnmodifiable_pattern() {

    }
  }

  /**
   * Verifies that an Iterator is unmodifiable.
   *
   * <p>This test only works with iterators that iterate over a finite set.
   */
  public static void assertIteratorIsUnmodifiable(Iterator<?> iterator) {
    while (iterator.hasNext()) {
      iterator.next();
      try {
        iterator.remove();
        fail("Remove on unmodifiable iterator succeeded");

    }
  }

  /**
   * Verifies that an Iterator is unmodifiable.
   *
   * <p>This test only works with iterators that iterate over a finite set.
   */
  public static void assertIteratorIsUnmodifiable(Iterator<?> iterator) {
    while (iterator.hasNext()) {
      iterator.next();
      try {
        iterator.remove();
        fail("Remove on unmodifiable iterator succeeded");

    return unmodifiable;
  }

  private static <T extends @Nullable Object> void assertUnmodifiableIterableInTandem(
      Iterable<T> unmodifiable, Iterable<T> modifiable) {
    UnmodifiableCollectionTests.assertIteratorIsUnmodifiable(unmodifiable.iterator());
    UnmodifiableCollectionTests.assertIteratorsInOrder(
        unmodifiable.iterator(), modifiable.iterator());
  }

  public void testInvertFrom() {