Junit test that fails if singleton getInstance () method is out of sync

I have this singelton database that I created and this Junit test that I created:

one-point

package SingeltonDBVersion1;

import GlobalSetting.User;

/****************************************************************************
 * This is the SingeltonDB. it warps the object DBconn according to the
 * Singleton pattern. it receive name and password (i.e. DBConn parameters) and
 * if it is the first time that a UserContorll try to get an instance it connect
 * to the database. After that, the DBConn instance will be return to the user.
 *****************************************************************************/
public class SingeltonDB {
    private static DBconnImpl db = null;
    private static SingeltonDB singalDb = null;
    boolean first = true;

    private SingeltonDB(String username, String password) {
        if (first) {
            try {
                System.out.println("first");
                Thread.sleep(5000);

            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            first = false;
        }
        db = new DBconnImpl();
    }

    public static SingeltonDB getInstance(String username, String password)
            throws Exception {
        if (db != null) {
            return singalDb;
        }

        singalDb = new SingeltonDB(username, password);
        System.out.println("The database is now open");
        db.connect(username, password);
        System.out.println("The database was connected");
        return singalDb;
    }

    public void create(String tableName) throws Exception {
        db.create(tableName);
    }

    public User query(String tableName, int userID) throws Exception {
        if (db == null) {
            System.out.println("Error: the database is not open");
            return null;
        }
        return (db.query(tableName, userID));
    }

    public void update(String tableName, User user) throws Exception {
        if (db == null) {
            System.out.println("Error: the database is not open");
            return;
        }
        db.update(tableName, user);
    }

    public void disconnect() throws Exception {
        db.disconnect();
    }

    public static void reset() throws Exception {
        db = null;
    }
}

      

        
        
        
      

    

Junit

package Tests;

import java.util.concurrent.CountDownLatch;

import org.junit.Test;

import SingeltonDBVersion1.SingeltonDB;


public class SingeltonDBVersion1Tests {

        @Test
        public synchronized void testSynch() throws Exception {
            int num=2;
            CountDownLatch doneSignal = new CountDownLatch(num);

            MySingeltonDB[] instances = new MySingeltonDB[num];
            for (int i = 0; i < num; i++) {
                instances[i]=new MySingeltonDB(doneSignal);

            }
            SingeltonDB.reset();
            for (int i = 0; i < num; i++) {
                instances[i].run();

            }
             doneSignal.await(); 
                for (int i = 0; i < num; i++) { 
                    for (int j = i; j < instances.length; j++) {
                        if (instances[i].getDB()!=instances[j].getDB())
                        {
                            throw (new Exception());
                        }
                    }
                }
        }


    class MySingeltonDB implements Runnable {
        SingeltonDB db;
        CountDownLatch doneSignal;

        public MySingeltonDB(CountDownLatch doneSignal) {
            this.db = null;
            this.doneSignal = doneSignal;
        }

        public SingeltonDB getDB() {
            return db;
        }

        @Override
        public void run() {
            try {
                this.db = SingeltonDB.getInstance("MyAccount", "123");
                doneSignal.countDown();
                System.out.println("----------------------------------------->"+db );
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

    }
}

      

        
        
        
      

    

What I'm trying to do here is create 2 instances of a singleton if and only if the singletonDB: getInstance () method is out of sync. but for some reason the singleton works correctly and returns one instance of the class even if I am not using a synchronized method.