How to add a addTestDevice in Android studio

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

ads:adSize="BANNER" 

ads code is errorring

This is the Code But .addTestDevice is erroring how can ı add addTestDevice This is the code thanks