### Question:
OmemoService implements OmemoCarbonCopyStanzaReceivedListener, OmemoMessageStanzaReceivedListener { public static OmemoService<?, ?, ?, ?, ?, ?, ?, ?, ?> getInstance() { if (INSTANCE == null) { throw new IllegalStateException("No OmemoService registered"); } return INSTANCE; } protected  OmemoService(); static OmemoService<?, ?, ?, ?, ?, ?, ?, ?, ?> getInstance(); static boolean isServiceRegistered(); OmemoStore<T_IdKeyPair, T_IdKey, T_PreKey, T_SigPreKey, T_Sess, T_Addr, T_ECPub, T_Bundle, T_Ciph> getOmemoStoreBackend(); @SuppressWarnings("unused") void setOmemoStoreBackend(
            OmemoStore<T_IdKeyPair, T_IdKey, T_PreKey, T_SigPreKey, T_Sess, T_Addr, T_ECPub, T_Bundle, T_Ciph> omemoStore); @Override void onOmemoCarbonCopyReceived(CarbonExtension.Direction direction,
                                          Message carbonCopy,
                                          Message wrappingMessage,
                                          OmemoManager.LoggedInOmemoManager managerGuard); @Override void onOmemoMessageStanzaReceived(Stanza stanza, OmemoManager.LoggedInOmemoManager managerGuard); void purgeDeviceList(OmemoManager.LoggedInOmemoManager managerGuard);  }### Answer:
@Test(expected = IllegalStateException.class) public void getInstanceFailsWhenNullTest() { OmemoService.getInstance(); }