*
   * <p>In this case, {@code collection} was not modified as a result of the {@code add()} call, and
   * the test will fail because the number of occurrences of {@code existingElement} is unchanged.
   *
   * @param elements expected additional contents of {@link #container}
   */
  protected final void expectAdded(E... elements) {
    List<E> expected = Helpers.copyToList(getSampleElements());
    expected.addAll(Arrays.asList(elements));

   *
   * <p>In this case, {@code collection} was not modified as a result of the {@code add()} call, and
   * the test will fail because the number of occurrences of {@code existingElement} is unchanged.
   *
   * @param elements expected additional contents of {@link #container}
   */
  protected final void expectAdded(E... elements) {
    List<E> expected = Helpers.copyToList(getSampleElements());
    expected.addAll(Arrays.asList(elements));