Iterator<String> iterator = singletonIterator("a");
    Set<String> set = copyOf(iterator);
    assertEquals(singleton("a"), set);
  }

  public void testCopyOf_iterator_oneElementRepeated() {
    Iterator<String> iterator = Iterators.forArray("a", "a", "a");
    Set<String> set = copyOf(iterator);
    assertEquals(singleton("a"), set);
  }