Is it possible to mock android services under unit tests?

Question

I'm trying to write unit tests for my android application and I want to mock my service class. I want to test some error behaviors in the service, such as connection errors or file not found.

To simplify my question, I started a new Android Project and created an Activity and a Service class:

MyAndroidProjectActivity.java

package br.org.venturus.android;

import android.app.Activity;
import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.ServiceConnection;
import android.os.Bundle;
import android.os.IBinder;
import android.view.View;
import android.widget.TextView;
import br.org.venturus.android.service.MyService;

public class MyAndroidProjectActivity extends Activity {
    private MyService service;
    private ServiceConnection mConnection = new ServiceConnection() {

        public void onServiceConnected(ComponentName className, IBinder binder) {
            service = ((MyService.MyBinder) binder).getService();

        }

        public void onServiceDisconnected(ComponentName className) {
            service = null;
        }
    };
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        {
            Intent service = new Intent(this, MyService.class);
            startService(service);

            bindService(service, mConnection, Context.BIND_AUTO_CREATE);
        }

    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        // stop MyService
        {
            Intent svc = new Intent(this, MyService.class);
            stopService(svc);
        }
    }

    public void doChange(View view) {
        TextView tv = (TextView) findViewById(R.id.tvHello);

        tv.setText(service.getNewString());
    }
}

MyService.java

package br.org.venturus.android.service;

import br.org.venturus.android.R;
import android.app.Service;
import android.content.Intent;
import android.os.Binder;
import android.os.IBinder;

public class MyService extends Service {

    private IBinder binder;

    public MyService() {
        this.binder = new MyBinder();
    }
    @Override
    public IBinder onBind(Intent intent) {
        return binder;
    }

    @Override
    public void onCreate() {
        super.onCreate();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();

    }

    public class MyBinder extends Binder {
        public MyService getService() {
            return MyService.this;
        }
    }

    public String getNewString() {
        return getString(R.string.change);
    }

}

And I created a new Android Test Project with this unit class:

MyAndroidProjectActivityTest.java

package br.org.venturus.android.test;

import android.test.ActivityInstrumentationTestCase2;
import android.test.UiThreadTest;
import android.widget.Button;
import android.widget.TextView;
import br.org.venturus.android.MyAndroidProjectActivity;
import br.org.venturus.android.R;

public class MyAndroidProjectActivityTest extends
        ActivityInstrumentationTestCase2<MyAndroidProjectActivity> {

    private MyAndroidProjectActivity mActivity;
    private TextView tvHello;
    private Button btChange;

    public MyAndroidProjectActivityTest() {
        super("br.org.venturus.android", MyAndroidProjectActivity.class);
    }

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

        // Get the activity and components
        {
            mActivity = this.getActivity();
            tvHello = (TextView) mActivity
                    .findViewById(br.org.venturus.android.R.id.tvHello);
            btChange = (Button) mActivity
                    .findViewById(br.org.venturus.android.R.id.btChange);
        }

    }

    public void testPreconditions() {
        assertNotNull(tvHello);
        assertNotNull(btChange);
    }

    @UiThreadTest
    public void testChangeButton() {
        assertEquals(tvHello.getText(), getActivity().getString(R.string.hello));
        btChange.performClick();
        assertEquals(tvHello.getText(), getActivity()
                .getString(R.string.change));
    }
}

When I run the unit tests, the pre conditions and the change button tests are fine. What I want to do, for instance, is to create a MyServiceMock and override the MyService.getNewString to return other value, and mock this object in the test.

Something like this:

MyServiceMock.java

package br.org.venturus.android.test.service;

import br.org.venturus.android.service.MyService;

public class MyServiceMock extends MyService {
    @Override
    public String getNewString() {      
        return "This is the new value!";
    }
}

Is that possible?

Answer 1

Yes, it's possible and I think the example of the MyServiceMock.java above is also an alternative.

There are a few mocking frameworks out there that you can use for this.

I have some experience with Mockito.

You can just mock the MyService class and specify that when the getNewString method is called, return a string "This is the new value!".

MyService myServiceMock = Mockito.mock(MyService.class);

Mockito.doReturn("This is the new value!").when(myServiceMock).getNewString();

You can also use the Mockito.doThrow() method to throw an exception when a mock method is called:

Mockito.doThrow(new RuntimeException()).when(mockedList).clear();

//following throws RuntimeException:
mockedList.clear();