* String a1 = peekingIterator.peek(); // returns "a"
   * String a2 = peekingIterator.peek(); // also returns "a"
   * String a3 = peekingIterator.next(); // also returns "a"
   * }
   *
   * <p>Any structural changes to the underlying iteration (aside from those performed by the
   * iterator's own {@link PeekingIterator#remove()} method) will leave the iterator in an undefined
   * state.

   * String a1 = peekingIterator.peek(); // returns "a"
   * String a2 = peekingIterator.peek(); // also returns "a"
   * String a3 = peekingIterator.next(); // also returns "a"
   * }
   *
   * <p>Any structural changes to the underlying iteration (aside from those performed by the
   * iterator's own {@link PeekingIterator#remove()} method) will leave the iterator in an undefined
   * state.

    Iterator<String> nonpeek = Lists.newArrayList("a", "b", "c").iterator();
    PeekingIterator<String> peek = peekingIterator(nonpeek);
    assertThat(nonpeek).isNotSameInstanceAs(peek);
    assertThat(peekingIterator(peek)).isSameInstanceAs(peek);
    assertThat(peekingIterator((Iterator<String>) peek)).isSameInstanceAs(peek);
  }

  public void testMergeSorted_stable_issue5773Example() {

    Iterator<String> nonpeek = Lists.newArrayList("a", "b", "c").iterator();
    PeekingIterator<String> peek = peekingIterator(nonpeek);
    assertThat(nonpeek).isNotSameInstanceAs(peek);
    assertThat(peekingIterator(peek)).isSameInstanceAs(peek);
    assertThat(peekingIterator((Iterator<String>) peek)).isSameInstanceAs(peek);
  }

  public void testMergeSorted_stable_issue5773Example() {