### Question:
ImmutableKeySet extends AbstractKeySet<K> { @Override public Iterator<K> iterator() { return immutableIterator(); } ImmutableKeySet(final TrieMap<K, ?> map); @Override Iterator<K> iterator(); @Override void clear(); @Override @SuppressWarnings("checkstyle:parameterName") boolean remove(final Object o); @Override @SuppressWarnings("checkstyle:parameterName") boolean retainAll(final Collection<?> c); @Override @SuppressWarnings("checkstyle:parameterName") boolean removeAll(final Collection<?> c);  }### Answer:
@Test public void testIterator() { assertFalse(set.iterator().hasNext()); }