@Before
  public void setUp() throws Exception {
    super.setUp();

    notifDao.purgeAll();

    List<String> keys = notifDao.getAggregationKeys();
    assertEquals(0, keys.size());

    keys = notifDao.getAggregationCompletedKeys();
    assertEquals(0, keys.size());
  }
  @Test
  public void testScan_nullKeys_assertEmptySet() throws Exception {

    AggregationDAO dao = mock(AggregationDAO.class);
    when(dao.getAggregationCompletedKeys()).thenReturn(null);

    final ConcurrentJPAAggregationRepository repo =
        new ConcurrentJPAAggregationRepository(notifDao);

    final Set<String> ids = repo.scan(context);

    assertEquals(0, ids.size());
  }