public CacheConfig<K, V> setAsyncBackupCount(int asyncBackupCount) {
        this.asyncBackupCount = checkAsyncBackupCount(backupCount, asyncBackupCount);
        return this;
    }
@Test(expected = IllegalArgumentException.class)
    public void setAsyncBackupCount_whenItsNegative() {
        CacheConfig config = new CacheConfig();
        config.setAsyncBackupCount(-1);
    }