### Question:
InstallerServiceImpl implements InstallerService { @Override public Optional<Installer> findByInstallerToken(String installerToken) { return installerDao.findByInstallerToken(installerToken); }  @Transactional @Override String save(NewRegistrationParam registrationInfo, Integer appReleaseId, Integer userId); @Override void update(Installer installer, UpdateRegistrationParam registrationInfo); @Override Optional<Installer> findByInstallerToken(String installerToken); @Override void delete(Installer installer);  }### Answer:
@Test public void find_by_installer_token_no_data() { Optional<Installer> installerOption = installerDao.findByInstallerToken("not-exist-installer-token"); assertThat(installerOption).isEmpty(); }