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Robolectric

Integrating RoboGuice and Robolectric

The RobolectricSample application includes an example of how to test Android applications that are built using the RoboGuice dependency injection framework. This article explains what we did and how you can add RoboGuice to your own projects.

The Sample Activity

For the most part RoboGuice will just work when injected instances of classes are exercised by unit tests, but with a little bit of work can inject those instances directly into our tests. As an example, we can start with this simple activity:

public class InjectedActivity extends GuiceActivity {
    @InjectResource(R.string.injected_activity_caption) String caption;
    @InjectView(R.id.injected_text_view) TextView injectedTextView;

    @Override protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.injected);
        injectedTextView.setText(caption);
    }
}

To get this to work you need to change your manifest to point to roboguice.application.GuiceApplication (or a subclass) and link with the RoboGuice library. We wrote the following test:

@Test
public void shouldAssignStringToTextView() throws Exception {
    injectedActivity.onCreate(null);
    TextView injectedTextView =
        (TextView) injectedActivity.findViewById(R.id.injected_text_view);
    assertEquals(injectedTextView.getText(), caption);
}

This test passes but the set up for it is ugly:

InjectedActivity injectedActivity;
String caption;
@Before
public void setUp() {
    injectedActivity = new InjectedActivity();
    Resources resources = injectedActivity.getResources();
    caption = resources.getString(R.string.injected_activity_caption);
}

Injecting Tests

With some changes to the test runner we can make it look like this:

    @Inject InjectedActivity injectedActivity;
    @InjectResource(R.string.injected_activity_caption) String caption;

In RobolectricSample we created a subclass of RobolectricTestRunner called InjectedTestRunner and extended it to ensure that instances of the test class were injected before the tests were run. RobolectricTestRunner has a method called prepareTest(Test test) that exists for the purpose of giving its subclasses access to the Test object just before each test. It can be used for injection as follows:

public class InjectedTestRunner extends RobolectricTestRunner {
    public InjectedTestRunner(Class<?> testClass) throws InitializationError {
        super(testClass);
    }

    @Override public void prepareTest(Object test) {
        GuiceApplication sampleApplication = (GuiceApplication) Robolectric.application;
        Injector injector = sampleApplication.getInjector();
        injector.injectMembers(test);
    }
}

It can be used in a @RunWith clause instead of RobolectricTestRunner:

@RunWith(InjectedTestRunner.class)
public class InjectedActivityTest {
...
}

Injecting Context Objects onto Tests

There are some types, such as Contexts that RoboGuice can’t inject without entering the context scope in the test runner’s prepareTest() method:

@Override public void prepareTest(Object test) {
    GuiceApplication sampleApplication = (GuiceApplication) Robolectric.application;
    Injector injector = sampleApplication.getInjector();
    ContextScope scope = injector.getInstance(ContextScope.class);
    scope.enter(sampleApplication);
    injector.injectMembers(test);
}

Now it is possible to inject a Context object onto the test:

@Inject Context context;
@Test
public void shouldBeAbleToInjectAContext() throws Exception {
    assertNotNull(context);
}

Next: Test Modules