System service testing

[Nike Dev]

How I can test a system service? In my case I need to test DevicePolicyManager. Below piece of my code:

public class DeviceAdministratorHelper {

    DevicePolicyManager devicePolicyManager;

    ComponentName adminComponentName;

    public DeviceAdministratorHelper(Context context) {

        devicePolicyManager = (DevicePolicyManager) context.getSystemService(Context.DEVICE_POLICY_SERVICE);

        adminComponentName = new ComponentName(context, AdminBroadcastReceiver.class);

    }

    public void lockDeviceNow() {

       devicePolicyManager.lockNow();

    }

}

Should I create a shadow class? Or what I should do?

[Johannes Elgh]

Cannot get this to work myself. Please post here if you got it to work!

[Nike Dev]

Guys from Robolectric, help me please. I really need your advice. 

I can not test class which contains some system service.

Now I use Robolectric 2.1

For example my class:

public class PlayTrackService extends Service {

    @Override

    public int onStartCommand(Intent intent, int flags, int startId) {

        _performPlaying();

        return START_NOT_STICKY;

    }

    private void _performPlaying(){

        AudioManager audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);

        audioManager.setSpeakerphoneOn(true);

        audioManager.setMode(AudioManager.MODE_IN_CALL );

        audioManager.setStreamVolume(AudioManager.STREAM_MUSIC, 3, 0);

        MediaPlayer mp = MediaPlayer.create(getApplicationContext(), R.raw.simple_track);

        mp.setLooping(true);

        mp.start();

    }

}

There is my test:

@Test

@Config(shadows = {ShadowAudioManager.class})

public void testOnStartCommand() throws Exception {

    PlayTrackService service = new PlayTrackService();

    int res = service.onStartCommand(new Intent(), Service.START_NOT_STICKY,1);

    assertEquals(Service.START_NOT_STICKY, res);

    service.onDestroy();

}

But when I run test I have NullPointerException when I try get AudioManager

in this string: AudioManager audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);

May be I have wrong way to perform test? Explain please how I can do this correctly