I/Ads: Ad failed to load : 2

Question

I'm trying to implement AdMob in my application, I'm getting the below error

My Error is :

 I/Ads: This request is sent from a test device.
 I/Ads: Ad failed to load: 2

Java code :

MobileAds.initialize(this,"ca-app-pub-3940256099942544~3347511713");
AdView adView=(AdView)findViewById(R.id.adv_id);

AdRequest adRequest = new AdRequest.Builder().addTestDevice(
AdRequest.DEVICE_ID_EMULATOR).build();
adView.loadAd(adRequest);

XML

ads:adUnitId="ca-app-pub-3940256099942544~3347511713"></com.google.android.gms.ads.AdView>