Acai

Acai makes it easy to write functional tests of your application with JUnit4 and Guice.

Acai makes it simple to:

• Inject the helper classes you need into tests
• Start any services needed by your tests
• Run between-test cleanup of these services
• Start up multiple services for testing in the right order
• Create test scoped bindings

Acai is designed for large functional tests of your application. For example it can help with writing tests which start your backend and frontend server in a self-contained mode with their dependencies faked out and then validates some key user scenarios with Webdriver to give you confidence your complete system works correctly. It can also be useful for tests which validate the integration of a small set of components. Note however that for smaller unit-tests we generally recommend you create the class under test manually rather than using Acai.

Installation

Add a dependency on com.google.acai:acai in your build system to fetch Acai automatically from Maven Central. For example, with Maven add the following to your dependencies in pom.xml:

<dependency>
  <groupId>com.google.acai</groupId>
  <artifactId>acai</artifactId>
  <version>1.1</version>
  <scope>test</scope>
</dependency>

See the artifact details on Maven Central for dependency information for other build systems or to simply download the jars.

Using Acai to inject a test

The simplest test using Acai doesn’t register any TestingService bindings at all, it just uses Acai to inject a test with a module:

@RunWith(JUnit4.class)
public class SimpleTest {
  @Rule public Acai acai = new Acai(MyTestModule.class);

  @Inject private MyClass foo;

  @Test
  public void checkSomethingWorks() {
    // Use the injected value of foo here
  }

  private static class MyTestModule extends AbstractModule {
    @Override protected void configure() {
      bind(MyClass.class).to(MyClassImpl.class);
    }
  }
}

Using Acai to start services

The real power of Acai comes when your production server is configured with Guice and you create an alternate test module which configures your server with heavyweight dependencies like databases replaced with local in-memory implementations. You could then start this server once for all tests in the suite. For example:

@RunWith(JUnit4.class)
public class ExampleFunctionalTest {
  @Rule public Acai acai = new Acai(MyTestModule.class);

  @Inject private MyServerClient serverClient;

  @Test
  public void checkSomethingWorks() {
    // Call the running server and test some behaviour here.
  }

  private static class MyTestModule extends AbstractModule {
    @Override protected void configure() {
      // Normal Guice modules which configure your
      // server with in-memory versions of backends.
      install(MyServerModule());

      install(TestingServiceModule.forServices(MyServerRunner.class));
    }
  }

  private static class MyServerRunner implements TestingService {
    @Inject private MyServer myServer;

    @BeforeSuite void startServer() {
      myServer.start().awaitStarted();
    }
  }
}

Note that when a module is passed to Acai in a rule any @BeforeSuite methods are only executed once per suite even if the same module is used in multiple Acai rules in multiple different test classes within that suite. This allows tests of the server to be structured into test classes according to the functionality being tested.

Test isolation

When sharing a locally running backend or fake between multiple test cases as above it’s often necessary to clear its state between each test in order to isolate tests from one another.

This can be achieved using an @AfterTest method in a TestingService. The following example clears all data in a local database between tests:

@RunWith(JUnit4.class)
public class ExampleFunctionalTest {
  @Rule public Acai acai = new Acai(MyTestModule.class);

  @Inject private MyServerClient serverClient;

  @Test
  public void checkSomethingWorks() {
    // Perform actions which write to the database here.
    // Any state will be cleared by MyFakeDatabaseWiper after each
    // test case.
  }

  private static class MyTestModule extends AbstractModule {
    @Override protected void configure() {
      install(MyFakeDatabaseModule());
      install(TestingServiceModule.forServices(MyFakeDatabaseWiper.class));
    }
  }

  private static class MyFakeDatabaseWiper implements TestingService {
    @Inject private MyFakeDatabse myFakeDatabase;

    @AfterTest void wipeDatabase() {
      myFakeDatabase.wipe();
    }
  }
}

Test scoped bindings

Occasionally you may wish to have one instance of a class per test and inject this instance in multiple places in the object graph. In this case Guice’s default instance scope will not do. Fortunately Acai provides a @TestScoped annotation which can be used to achieve exactly this.

For example we may define a module for using Webdriver (a popular browser automation tool) in our tests like so:

class WebdriverModule extends AbstractModule {
  private static final Duration MAX_WAIT = Duration.standardSeconds(5);

  @Override
  protected void configure() {
    install(new TestingServiceModule() {
      @Override protected void configureTestingServices() {
        bindTestingService(WebDriverQuitter.class);
      }
    });
  }

  @Provides
  @TestScoped
  WebDriver provideWebDriver() {
    // Provide the driver here; precisely one instance will be
    // created per test case.
  }

  @Provides
  WebDriverWait provideWait(WebDriver webDriver) {
    return new WebDriverWait(webDriver, MAX_WAIT.getStandardSeconds());
  }

  static class WebDriverQuitter implements TestingService {
    @Inject Provider<WebDriver> webDriver;

    @AfterTest void quitWebDriver() throws Exception {
      // Calling get on the Provider here returns the instance
      // for the test case which we are currently tearing down.
      webDriver.get().quit();
    }
  }
}

One important point to note when using @TestScoped bindings is that TestingService instances are instantiated once for all tests outside of test scope. Therefore if you wish to access @TestScoped bindings in a @BeforeTest or @AfterTest method you should inject a Provider and call get on it within those methods as shown in the above example.

When not to use TestScoped

Note that while @TestScoped works well for helpers injected only into tests (such as the WebDriver instance in the above example) for fakes and other objects which are shared with the system under test it is usually simpler to use a single instance and reset its state with a TestingService (see Test isolation). This technique avoids some of the limitations of @TestScoped such as the fact it can only be injected on the test thread or child threads of the test and makes it possible to inject the instance into objects whose lifetime is longer than that of an individual test.

Services which depend upon each other

If the services you need to start for tests must be started in a specific order you can express this using the @DependsOn annotation.

For example:

@RunWith(JUnit4.class)
public class ExampleFrontendWebdriverTest {
  @Rule public Acai acai = new Acai(MyTestModule.class);

  @Inject private SomeFrontendFeaturePageObject featurePage;

  @Test
  public void checkSomethingWorks() {
    // Test the frontend client using the webdriver page
    // object here.
  }

  private static class MyTestModule extends AbstractModule {
    @Override protected void configure() {
      // Normal Guice modules which configure your
      // server with in-memory versions of servers and
      // a test module configuring a webdriver client.
      install(MyServerModule());
      install(MyFakeDatabaseModule());
      install(WebDriverModule());

      install(new TestingServiceModule() {
        @Override protected void configureTestingServices() {
          bindTestingService(MyFrontendRunner.class);
          bindTestingService(MyBackendRunner.class);
        }
      });
    }
  }

  @DependsOn(MyBackendRunner.class)
  private static class MyFrontendRunner implements TestingService {
    @Inject private MyFrontendServer myFrontendServer;

    @BeforeSuite void startServer() {
      myFrontendServer.start().awaitStarted();
    }
  }

  private static class MyBackendRunner implements TestingService {
    @Inject private MyBackendServer myBackendServer;

    @BeforeSuite void startServer() {
      myBackendServer.start().awaitStarted();
    }
  }
}

In the above example MyFrontendRunner is annotated @DependsOn(MyBackendRunner.class) which will cause Acai to start the backend server before starting the frontend.

API

As shown in the above examples Acai has a relatively small API surface. Firstly, and most importantly, there is the Acai rule class itself which is used as a JUnit4 @Rule and is passed a module class to be used to configure the test.

The module class passed to the Acai constructor may optionally use TestingServiceModule to bind one or more TestingService implementations.

The TestingService interface is purely a marker to allow Acai to know which classes provide testing services. To actually do anything implementations of this interface should add zero argument methods annotated with one of @BeforeSuite, @BeforeTest or @AfterTest. These methods will be run before the suite, before each test or after each test respectively. You may add as many methods annotated with these annotations as you wish to a TestingService; Acai will find and run them all when appropriate.

For more advanced use-cases where instance scope is not sufficient the @TestScoped annotation can be used to create one instance of a class per test case.

Finally a TestingService implementation can be annotated @DependsOn to signal its @BeforeSuite and @BeforeTest methods need to be run after those of another TestingService. This provides a simple declarative mechanism to order service startup in tests.

Refer to the examples above to see the API in action.

Contributing

We’d love to accept your patches and contributions to this project. There are a just a few small guidelines you need to follow. See the CONTRIBUTING.md file for more information.

Disclaimer

This is not an official Google product.