### Question:
MutableIterator extends AbstractIterator<K, V> { @Override public void remove() { if (lastReturned == null) { throw new IllegalStateException(); } mutable.remove(lastReturned.getKey()); lastReturned = null; } MutableIterator(final MutableTrieMap<K, V> map); @Override void remove();  }### Answer:
@Test public void testRemoveWithoutNext() { assertThrows(IllegalStateException.class, () -> it.remove()); }