RelativeLayout layout = new RelativeLayout(this);
    AndroidApplicationConfiguration config = new AndroidApplicationConfiguration();
    View gameView = initializeForView(new MainGame(), config);

    layout.addView(gameView);


    adView = new AdView(this);

    adView.setAdListener(new AdListener() {
        @Override
        public void onAdLoaded() {
            System.out.println("LOAD");
        }
    });
    adView.setAdSize(AdSize.SMART_BANNER);
    adView.setAdUnitId("ca-app-xxx-xxxxxxxxxx/xxxxxxxxxx");

    AdRequest.Builder builder = new AdRequest.Builder();
    RelativeLayout.LayoutParams adParams = new RelativeLayout.LayoutParams(
            RelativeLayout.LayoutParams.WRAP_CONTENT,
            RelativeLayout.LayoutParams.WRAP_CONTENT
    );
    layout.addView(adView, adParams);
    adView.loadAd(builder.build());

    setContentView(layout);

Nada é mostrado, nenhum anúncio, por que eu adicionei também no build.gradle (Projeto: projectN) compile "com.google.android.gms: play-services-ads: $ admobVersion"

Usando o Ubuntu 16.04, android-studio