* source Iterable, unless that Iterator is unmodifiable.
   */
  protected abstract I newTargetIterator();

  /**
   * Override this to verify anything after running a list of Stimuli.
   *
   * <p>For example, verify that calls to remove() actually removed the correct elements.
   *
   * @param elements the expected elements passed to the constructor, as mutated by {@code

   * source Iterable, unless that Iterator is unmodifiable.
   */
  protected abstract I newTargetIterator();

  /**
   * Override this to verify anything after running a list of Stimuli.
   *
   * <p>For example, verify that calls to remove() actually removed the correct elements.
   *
   * @param elements the expected elements passed to the constructor, as mutated by {@code