@Test
  public void testStartUpWithoutMetadataExists() {
    accountService = mockHelixAccountServiceFactory.getAccountService();
    // At time zero, no account metadata exists.
    assertEquals("The number of account in HelixAccountService is incorrect after clean startup", 0,
        accountService.getAllAccounts().size());
  }
Tests a clean startup of {@link HelixAccountService}, when the corresponding {@code ZooKeeper} does not
have any {@link ZNRecord} on it.
ambry-account/src/test/java/com/github/ambry/account/HelixAccountServiceTest.java