### Question:
MutableKeySet extends AbstractKeySet<K> { @Override @SuppressWarnings("checkstyle:parameterName") public boolean remove(final Object o) { return map().remove(o) != null; } MutableKeySet(final MutableTrieMap<K, ?> map); @Override Iterator<K> iterator(); @Override void clear(); @Override @SuppressWarnings("checkstyle:parameterName") boolean remove(final Object o);  }### Answer:
@Test public void testRemove() { assertFalse(set.remove(VALUE)); assertEquals(1, map.size()); assertEquals(1, set.size()); assertTrue(set.remove(KEY)); assertTrue(map.isEmpty()); }
@Test public void testRemoveNull() { assertThrows(NullPointerException.class, () -> set.remove(null)); }