@Test
  public void testGetLatestAccountMap_BackupFilesAllWithoutVersion() throws IOException {
    final long baseModifiedTime = System.currentTimeMillis() / 1000 - 100;
    final long interval = 2;
    final int count = maxBackupFile / 2;
    String[] filenames = createBackupFilesWithoutVersion(accountBackupDir, count, baseModifiedTime, interval, false);
    saveAccountsToFile(Collections.singleton(refAccount), accountBackupDir.resolve(filenames[filenames.length - 1]));

    BackupFileManager backup =
        new BackupFileManager(accountServiceMetrics, config.backupDir, config.maxBackupFileCount);
    Collection<Account> obtained = backup.getLatestAccounts(0);
    assertNull("No state should be loaded from backup file from old format", obtained);
    assertFalse("Backup should not be empty since there are files from old format", backup.isEmpty());
    assertEquals(backup.size(), count);
  }
Test getLatestAccounts function when all the backup files are files without version number.
@throws IOException if I/O error occurs
ambry-account/src/test/java/com/github/ambry/account/BackupFileManagerTest.java