public CacheConfig<K, V> setBackupCount(int backupCount) {
        this.backupCount = checkBackupCount(backupCount, asyncBackupCount);
        return this;
    }
@Test(expected = IllegalArgumentException.class)
    public void setBackupCount_whenTooLarge() {
        CacheConfig config = new CacheConfig();
        config.setBackupCount(200); //max allowed is 6..
    }