Agfdhyk

I have a class like this. The start method will be called in another class(like pre-load class)

public class Processor implements Runnable{



   private PersistantQueue<object> m_persistentQueue;

   private Thread m_thread;



  //this class is a singleton class



   protected int getQueueSize() {

       return m_persistentQueue.size();

   }





   protected void addToQueue(Object object) {

       m_persistentQueue.add(object);

   }





   public void start() {     

     m_persistentQueue = new PersistantQueue<object>("queueName");

     m_thread = new Thread(new Processor());

     m_thread.start();

   }

 //run method......

}

And this is the unit test

  public class AuditEventProcessorTest {



      private Processor m_processor



    @Before

      public void setup() {

         m_Processor = Processor.getProcessorInstance();

         m_Processor.start();

    }

    @After

      //some cleanup after adding items to the queue





   @Test

     public void addToQueue_addSuccessfully() {

     m_Processor.addToQueue(someMockObject);

     assertEquals(1, m_Processor.getQueueSize());

      }

   }

I call the real method to add items to the queue. But now I want to mock the queue just test logic. I don't want to add items to the queue in the unit test. How can I properly mock the queue? Try to mock but get null pointer exception. I can only use Mockito. Please help me. Thanks!

SingleTon pattern are kind of complex to unit-test. In your case it is more complex as you have completely hidden queue creation logic. Would suggest to do some refactoring and allow injection and use spring(if using spring) managed singleton(if you need singleton only) beans. Dependency Injection makes unit testing much easier.

If you want to carry on with same implementation as in question then below is the example but you need to use PowerMockito.

@RunWith(PowerMockRunner.class)

@PrepareForTest(Processor.class)

public class ProcessorTest {



    private Processor processor;

    @Test

    public void test() throws Exception {

        Processor processor = Processor.getInstance();

        ArrayBlockingQueue arrayBlockingQueue = Mockito.mock(ArrayBlockingQueue.class);



        PowerMockito.whenNew(ArrayBlockingQueue.class).withAnyArguments().thenReturn(arrayBlockingQueue);



        processor.start();



        //now you have successfully inject mocked arrayBlockQueue in Processor and can play around with it as usual with any mock object.

    }

}

Just ArrayBlockingQueue with your PersistantQueue.

Hope this helps.