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README.md

Instrumentation Testing with Dagger, Mockito, and Espresso

Historically, testing on Android has not been easy, but many awesome projects have emerged which, in combination, have made testing much simpler. We have found that a great combination of coffee, booze, and weaponry that eases this pain. Specifically, Espresso, Mockito, and Dagger 2.

Dependency Injection

Dependency injection is the cornerstone of what makes much of the Circle Android app testable. Unfortunately, many Android framework classes (e.g. Activity) are not instantiated in your code. This makes it difficult to supply dependencies via constructors (e.g. an instance of an API class to your Activity) and presents a real challenge when trying to write functional tests.

Dagger 2

There are a number of dependency injection libraries available for Java, but there is really only one worth considering for Android. Dagger 2. Dagger 2 performs depenency injection at compile time which means:

  • Injections will fail at compile time instead run time which lets your catch mistakes more quickly.
  • There is no performance hit because injections are not performed using relfection like other dependency injection frameworks.
  • No more proguard exceptions for injected code which both saves the developer time (and tears) and increases security.

Because Dagger 2's API and motiviation is very similar to the original Dagger and there are already several great introductions to Dagger, we're going just jump right into the code. I highly recommend the following resources for the uninitiated.

Note: Although Dagger 2 is technically considered pre-alpha by it's creators, it is actually being used in critical production systems and the pre-alpha status is because there may be some small API changes to come.

A Simple Testable App

In our simple app, there is an activity that allows a user to authenticate some credentials. In our tests, we will verify that the activity under test behaves correctly depending on the API response returned. If the API confirms that the credentials are valid, the activity should launch a new activity. If the credentials are invalid, the activity should show an error message.

However, we want to just test the activity's behavior and not perform an end to end test. We don't actually want to make API calls because they slow down tests and we are only concerned that the activity's implementation is correct. By using mocks and dependency injection, we can write better tests more easily and without having to create weird accessor methods in our activities to support testing.

Setting up Dagger

Your build.gradle file will look sometihng like this.

In it you'll notice:

  • We add the Sonatype Snapshot Respository to import our Dagger 2 dependencies since it has not yet been published to Maven Central. Also we import a gradle plugin called Android-Apt which helps Android Studio detect the classes Dagger 2 generates.
  • We import Mockito and some libraries to make it play nice with Android's dexing. We import these only into our debug build, because the debug build is the default build that instrumentation tests are run against.
  • And lastly, we import Espresso 2 from the Android Support Library (make sure you have updated your local Android Support repository from the SDK manager).
buildscript {
    repositories {
        mavenCentral()
    }

    dependencies {
        // This plugin helps Android Studio find Dagger's generated classes
        classpath 'com.neenbedankt.gradle.plugins:android-apt:1.4'
    }
}
apply plugin: 'com.android.application'
// apply the Android-Apt plugin to our project
apply plugin: 'com.neenbedankt.android-apt'

repositories {
    // Currently, Dagger 2 is published to Sonatype's maven repo
    maven { url "https://oss.sonatype.org/content/repositories/snapshots/" }
}

android {
    compileSdkVersion 21
    buildToolsVersion '21.1.1'

    defaultConfig {
        minSdkVersion 14
        targetSdkVersion 21
        versionCode 1
        versionName '1.0.0'
        applicationId 'com.circle.sample'
    }
}

dependencies {
    // Dagger 2 dependencies
    compile 'com.google.dagger:dagger:2.0-SNAPSHOT'
    apt 'com.google.dagger:dagger-compiler:2.0-SNAPSHOT'
    provided 'org.glassfish:javax.annotation:10.0-b28' // adds the @Generated annoation that Android lacks

    // Mockito Dependencies
    debugCompile 'com.google.dexmaker:dexmaker-mockito:1.0'
    debugCompile 'com.google.dexmaker:dexmaker:1.0'
    debugCompile 'org.mockito:mockito-core:1.10.17'

    // Espresso 2 Dependencies
    androidTestCompile 'com.android.support.test.espresso:espresso-core:2.0'
    androidTestCompile 'com.android.support.test:testing-support-lib:0.1'
}

Defining our Dependency Graphs

In our example application, we have an Api class that we want to inject into our Activities. For the sake of a simple example, our Api pretends to make a network call, but we will actually mock out this code later when testing.

public class Api {

    public Observable<Boolean> login(String username, String password) {
        // imagine an actual Api call here
        return Observable.just(true);
    }
}
Modules

Modules are classes that define a set of providers (methods annotated with @Provides) and the dependency graph is created by a Component and the set of Modules it includes. Here are two very simple Modules which we will use in the project.

DataModule provides a single instance of our Api class. We will use this when compiling our release build variant.

@Module
public final class DataModule {

    @Provides @Singleton
    public Api provideApi() {
        return new Api();
    }

}

DebugDataModule is similar to DataModule, but it can be initialized to return a mock of the Api class that we can use for testing. It is especially important that we use the @Singleton annotation on the provides method because it ensures that our test class and the class being tested receive the same variable instance. This module is used in our debug build variant.

@Module
public final class DebugDataModule {

    private final boolean mockMode;

    public DebugDataModule(boolean provideMocks) {
        mockMode = provideMocks;
    }

    @Provides @Singleton
    Api provideApi() {
        if (mockMode) {
            return Mockito.mock(Api.class);
        } else {
            return new Api();
        }
    }

}

If you are coming from Dagger 1, the modules are now simpler. Modules no longer need to define injectable classes or the modules they include. This is done by Components.

Components

Component interfaces define the collection of modules that will be used to construct the dependency graph and the classes it can inject dependencies into.

The Dagger compiler will generate a class Dagger_<ComponentName> (e.g. Dagger_Graph is generated from our interface Graph). Dagger_Graph is a class that contains the full dependency graph you have defined and knows how to inject into the classes we've declared injects() methods for.

The release variant

@Singleton
@Component(modules = {DataModule.class})
public interface Graph {

    void inject(BaseActivity activity);

    public final static class Initializer {
        public static Graph init(boolean mockMode) {
            return Dagger_Graph.builder()
                    .build();
        }
    }
}

The debug variant

@Singleton
@Component(modules = {DebugDataModule.class})
public interface Graph {

    void inject(BaseActivity activity);
    void inject(InjectedActivityTest test);

    public final static class Initializer {
        public static Graph init(boolean mockMode) {
            return Dagger_Graph.builder()
                    .debugDataModule(new DebugDataModule(mockMode))
                    .build();
        }
    }
}

To create an instance of your graph, the generated class has a builder. You'll notice in the release variant that we do not pass in an instance of the DataModule, but in the debug variant we do. The builder will initilize the modules it includes if the module's constructor does not require any parameters. Otherwise, the builder generates methods matching its modules and you must pass an instance in yourself.

The key difference to notice here is that release variant uses DataModule and the debug variant uses the DebugDataModule. The DebugDataModule will act normally unless when we initialize it, we put it in mock mode.

Injecting Dependencies

We create instances of our graph when start the app and access it from the Application and access it from classes though our App's static accessor. e.g. App.getInstance().graph().

public class App extends Application {

    private static App sInstance;
    private Graph graph;

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

        sInstance = this;
        graph = Graph.Initializer.init(false);
    }

    public static App getInstance() {
        return sInstance;
    }

    public Graph graph() {
        return graph;
    }

    public void setMockMode(boolean useMock) {
        graph = Graph.Initializer.init(useMock);
    }

}

In our example we have a BaseActivity that all other activities inherit from, and this is where we will do the injection.

public abstract class BaseActivity extends Activity {
    @Inject
    Api mApi;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        App.getInstance().graph().inject(this);
    }

    protected Api getApi() {
        return mApi;
    }
}

Writing Activity Tests

The final piece of the puzzle, injecting mocks into our ActivityInstrumentationTestCase2. All we have to do is get an instance of our App, tell it recreate our dependency graph in mock mode, and then inject the mocks into our test case so that we can manipulate them.

public class InjectedBaseActivityTest<T extends BaseActivity> extends ActivityInstrumentationTestCase2<T> {
    @Inject
    Api mockApi;

    public InjectedBaseActivityTest(Class<T> activityClass) {
        super(activityClass);
    }

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

        App app = (App) getInstrumentation().getTargetContext().getApplicationContext();
        app.setMockMode(true);
        app.graph().inject(this);
    }

    @Override
    protected void tearDown() throws Exception {
        App.getInstance().setMockMode(false);
    }
}

We recommend Espresso for writing UI tests, but you can use whatever you like. Espresso has a concise API and handles waits, sleeps, syncs, and polls. This greatly speeds up test writing and running.

So when we test an activity, we just define the mocking behavior that we want from the dependency we share with our Activity under test. Then confirm that the activity behaved this way. In this example, we have an Activity that has two text fields that performs a log in request. We want to test that it starts the right activity with a successful response or shows an error message if it fails.

public class MainActivityTest extends InjectedBaseActivityTest<MainActivity> {
    public MainActivityTest() {
        super(MainActivity.class);
    }

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

        getActivity();
    }

    public void testLoginSuccess() {
        when(mockApi.login("real@user.com", "secret")).thenReturn(Observable.just(true));

        ActivityMonitor monitor = getInstrumentation().addMonitor(AccountActivity.class.getName(), null, true);

        onView(withId(R.id.username)).perform(typeText("real@user.com"));
        onView(withId(R.id.password)).perform(typeText("secret"));
        onView(withId(R.id.button)).perform(click());

        assertEquals(1, monitor.getHits());

        getInstrumentation().removeMonitor(monitor);
    }

    public void testLoginFailure() {
        when(mockApi.login("real@user.com", "secret")).thenReturn(Observable.just(false));

        onView(withId(R.id.username)).perform(typeText("real@user.com"));
        onView(withId(R.id.password)).perform(typeText("secret"));
        onView(withId(R.id.button)).perform(click());

        onView(withText(getActivity().getString(R.string.error_invalid_credentials)))
                .check(matches(isDisplayed()));
    }
}

Summary

If you want to see what this looks like altogether, check out our sample project. To run the tests, start up an emulator and run ./gradlew cAT from your terminal.Hopefully this will get you on your way to integrating the new, awesome version of Dagger and start writing more tests for your projects.

This is just one use of dependency injection, but Jake Wharton's u2020 project shows off a lot of the great uses for Dagger in your project and it has been a great resource for us.

Cheers!