public String hashDirectoryId(final String cleartextDirectoryId) {
        if(!directoryIdCache.contains(cleartextDirectoryId)) {
            directoryIdCache.put(cleartextDirectoryId, impl.hashDirectoryId(cleartextDirectoryId));
        }
        return directoryIdCache.get(cleartextDirectoryId);
    }
@Test
    public void TestHashDirectoryId() {
        final FileNameCryptor mock = mock(FileNameCryptor.class);
        final CryptorCache cryptor = new CryptorCache(mock);
        when(mock.hashDirectoryId(anyString())).thenReturn("hashed");
        assertEquals("hashed", cryptor.hashDirectoryId("id"));
        assertEquals("hashed", cryptor.hashDirectoryId("id"));
        verify(mock, times(1)).hashDirectoryId(anyString());
        verifyNoMoreInteractions(mock);
    }