private void populateAccountService() throws AccountServiceException {
    accountService.clear();
    accountService.updateAccounts(Lists.newArrayList(refAccount, InMemAccountService.UNKNOWN_ACCOUNT));
  }
Prepopulates the {@link AccountService} with a reference {@link Account} and {@link InMemAccountService#UNKNOWN_ACCOUNT}.
ambry-frontend/src/test/java/com/github/ambry/frontend/FrontendRestRequestServiceTest.java