List<@Nullable String> list = newArrayList("a", null, "b", null, "a", null);
    assertEquals(2, frequency(list.iterator(), "a"));
    assertEquals(1, frequency(list.iterator(), "b"));
    assertEquals(0, frequency(list.iterator(), "c"));
    assertEquals(0, frequency(list.iterator(), 4.2));
    assertEquals(3, frequency(list.iterator(), null));
  }

  @GwtIncompatible // slow (~4s)

    List<@Nullable String> list = newArrayList("a", null, "b", null, "a", null);
    assertEquals(2, frequency(list.iterator(), "a"));
    assertEquals(1, frequency(list.iterator(), "b"));
    assertEquals(0, frequency(list.iterator(), "c"));
    assertEquals(0, frequency(list.iterator(), 4.2));
    assertEquals(3, frequency(list.iterator(), null));
  }

  @GwtIncompatible // slow (~4s)

   * iterator will be left exhausted: its {@code hasNext()} method will return {@code false}.
   *
   * @see Collections#frequency
   */
  public static int frequency(Iterator<?> iterator, @CheckForNull Object element) {
    int count = 0;
    while (contains(iterator, element)) {

func createTestInput(n int) []byte {
	input := make([]byte, n)
	for i := range input {
		// 101 and 251 are arbitrary prime numbers.
		// The idea is to create an input sequence
		// which doesn't repeat too frequently.
		input[i] = byte(i % 251)
		if i%101 == 0 {
			input[i] ^= byte(i / 101)
		}
	}
	return input
}

func TestReaderWriteTo(t *testing.T) {
	input := createTestInput(8192)

		groupSet.Add(k)
		return true
	})

	return groupSet.ToSlice(), nil
}

// ListGroups - lists groups. Since this is not going to be a frequent
// operation, we fetch this info from storage, and refresh the cache as well.
func (store *IAMStoreSys) ListGroups(ctx context.Context) (res []string, err error) {
	cache := store.lock()
	defer store.unlock()