public Collection<V> remove(K key)
    {
        List<V> removed = data.remove(key);
        if (removed != null) {
            for (V val : removed) {
                inverse.remove(val);
            }
        }
        return removed;
    }
@Test
    public void testRemoveWrongKey()
    {
        Collection<Integer> removed = map.remove(1L);
        assertThat(removed, is(Collections.singletonList(42)));

        assertSize(0);
    }