### Question:
HubBlacklistDAOFileImpl implements HubBlacklistDAO, ResourceListener { @Override public BlacklistedHub findBlacklistedHubByCertSn(String certSn) { return certSn == null ? null : getCachedData().get(certSn); } HubBlacklistDAOFileImpl(); @PostConstruct void init(); @Override BlacklistedHub findBlacklistedHubByCertSn(String certSn); @Override BlacklistedHub save(BlacklistedHub hub); @Override void delete(BlacklistedHub hub); @Override void onChange();  }### Answer:
@Test public void testFindBlacklistedHubByCertSn() { String cert = "testcertSn1"; BlacklistedHub fromDb = hubBlacklistDAO.findBlacklistedHubByCertSn(cert); assertNotNull(fromDb); assertEquals(cert, fromDb.getCertSn()); }