### Question:
ImmutableKeySet extends AbstractKeySet<K> { @Override @SuppressWarnings("checkstyle:parameterName") public boolean remove(final Object o) { throw unsupported(); } 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 testRemove() { assertThrows(UnsupportedOperationException.class, () -> set.remove(new Object())); }