assertNotSame(peek, nonpeek);
    assertSame(peek, peekingIterator(peek));
    assertSame(peek, peekingIterator((Iterator<String>) peek));
  }

  public void testMergeSorted_stable_issue5773Example() {
    ImmutableList<TestDatum> left = ImmutableList.of(new TestDatum("B", 1), new TestDatum("C", 1));
    ImmutableList<TestDatum> right = ImmutableList.of(new TestDatum("A", 2), new TestDatum("C", 2));