}

  public void test_contains_null_no() {
    Iterator<String> set = asList("a", "b").iterator();
    assertFalse(Iterators.contains(set, null));
  }

  public void testGetOnlyElement_noDefault_valid() {
    Iterator<String> iterator = singletonList("foo").iterator();
    assertEquals("foo", getOnlyElement(iterator));
  }

  public void testGetOnlyElement_noDefault_empty() {