}

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

  public void testGetOnlyElement_noDefault_empty() {
    Iterator<String> iterator = emptyIterator();
    assertThrows(NoSuchElementException.class, () -> getOnlyElement(iterator));
  }