android - Async Task - Android Instrumentaion Unit testing - Exception - Only thread created can update the asynctask

Question

This is my Asnyc task class

class EndpointsAsyncTask extends AsyncTask<Pair<Context, String>, Void, String> {
    private static MyApi myApiService = null;
    private Context context;

    private static final String TAG = "EndpointsAsyncTask";
    private MainActivity activity;

    private ProgressBar mProgressBar;

    private Exception mError = null;

    private JsonGetTaskListener mListener = null;

    InterstitialAd mInterstitialAd;

    public EndpointsAsyncTask setListener(JsonGetTaskListener listener) {
        this.mListener = listener;
        return this;
    }

    public static interface JsonGetTaskListener {
        public void onComplete(String jsonString, Exception e);
    }

    public EndpointsAsyncTask(MainActivity activity,ProgressBar mProgressBar){
        this.activity = activity;
        this.mProgressBar= mProgressBar;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        //   mProgressBar = new ProgressBar(this.activity);

        mInterstitialAd = new InterstitialAd(this.activity);
        mProgressBar.setVisibility(View.VISIBLE);
    }

    @Override
    protected String doInBackground(Pair<Context, String>... params) {
        if(myApiService == null) {  // Only do this once

            // end options for devappserver
            MyApi.Builder builder = new MyApi.Builder(AndroidHttp.newCompatibleTransport(), new AndroidJsonFactory(), null)
                .setRootUrl("https://backendversionone.appspot.com/_ah/api/");
  //      https://endpoint-backend-1056.appspot.com/_ah/api/


            myApiService = builder.build();
        }

        context = params[0].first;
        String name = params[0].second;

        try {
            return myApiService.sayHi(name+"check").execute().getData();
        } catch (IOException e) {
            return e.getMessage();
        }
    }

    @Override
    protected void onPostExecute(String result) {


       // Toast.makeText(context, result, Toast.LENGTH_LONG).show();

       // mProgressBar.setVisibility(View.GONE);
        if (this.mListener != null)
        this.mListener.onComplete(result, mError);

        mProgressBar.setVisibility(View.GONE);

        Intent myIntent = new Intent(context, LibraryMainActivity.class);
        myIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
        myIntent.putExtra("joke", result);
        context.startActivity(myIntent);


    }
}

Im trying to test my Async task from test class

Find my class below. public class MainActivityTest extends ActivityInstrumentationTestCase2 {

private MainActivity mMainActivity;
private TextView mFirstTestText;

ProgressBar pbar;

String mJsonString = null;
Exception mError = null;
CountDownLatch signal = null;

public MainActivityTest() {
    super(MainActivity.class);
}

@Override
protected void setUp() throws Exception {
    super.setUp();
    mMainActivity = getActivity();

    signal = new CountDownLatch(1);



}

@Override
protected void tearDown() throws Exception {
    super.tearDown();
    signal.countDown();
}
@MediumTest
public void testcheck(){

    Log.d("Testing baby", "Testcheck");
    Log.d("Testing baby","Testcheck");
    Log.d("Testing baby", "Testcheck");
    final Button sendToReceiverButton = (Button)
            mMainActivity.findViewById(R.id.buttontelljoke);



    assertNotNull(sendToReceiverButton);
}
@SmallTest
public void testchecks(){

    Log.d("Testing baby", "Testcheck");
    Log.d("Testing baby","Testcheck");
    Log.d("Testing baby", "Testcheck");
    final Button sendToReceiverButton = (Button)
            mMainActivity.findViewById(R.id.buttontelljoke);

    assertNotNull(sendToReceiverButton);
}
@MediumTest
public void testasyncTaskTest(){

    pbar = (ProgressBar)mMainActivity.findViewById(progressBar1);

    try {

        EndpointsAsyncTask jokeTask = new EndpointsAsyncTask(mMainActivity,pbar);
        jokeTask.setListener(new EndpointsAsyncTask.JsonGetTaskListener() {
            @Override
            public void onComplete(String jsonString, Exception e) {
                mJsonString = jsonString;
                mError = e;
                signal.countDown();
            }
        }).execute((new Pair<Context, String>(getActivity(), "")));
        signal.await();


        assertNotNull(mJsonString);





    } catch (Exception e){
        fail("Timed out");
    }
}


protected Fragment waitForFragment(String tag, int timeout) {
    long endTime = SystemClock.uptimeMillis() + timeout;
    while (SystemClock.uptimeMillis() <= endTime) {

        Fragment fragment = getActivity().getSupportFragmentManager().findFragmentByTag(tag);
        if (fragment != null) {
            return fragment;
        }
    }
    return null;
}

When running the test case , This line throws exception - Only the created thread can update the Async task

 jokeTask.setListener(new EndpointsAsyncTask.JsonGetTaskListener() {
            @Override
            public void onComplete(String jsonString, Exception e) {
                mJsonString = jsonString;
                mError = e;
                signal.countDown();
            }
        }).execute((new Pair<Context, String>(getActivity(), "")));
        signal.await();

But running the test when my phone is locked, I dont get exception and works fine.

How can i fix this issue.