TestNG has allowed users to control the instantation of their objects for a while now (around 2007).

This is enabled by the IObjectFactory interface:

public interface IObjectFactory extends Serializable {
  Object newInstance(Constructor constructor, Object... params);
}

Implement this interface, let TestNG know about your implementation and whenever TestNG needs to instantiate a test class, it will call the newInstance method of your object factory. This allows for a lot of flexibility, and interestingly, this interface appeared in the TestNG distribution long before Dependency Injection became as popular as it is today.

IObjectFactory has been very useful to TestNG users throughout the years, but the emergence of Dependency Injection has made its existence even more important. More and more TestNG users want to inject their test classes with DI frameworks, and over the past few months, I have noticed a sharp increase in Guice users.

IObjectFactory obviously works great with Guice (and Hani and I documented this extensively in our book) but the increased number of questions on the mailing-list prompted me to wonder if I couldn’t make this easier on Guice users.

As it turns out, the answer is yes.

Meet my little new friend, the guiceModule attribute:

@Test(guiceModule = GuiceExampleModule.class)
public class GuiceTest {

  @Inject
  ISingleton m_singleton;

  @Test
  public void singletonShouldWork() {
    m_singleton.doSomething();
  }
}

And that’s it! No need for IObjectFactory or modifying your build files, everything you need is contained in this new guiceModule attribute of the @Test annotation.

Obviously, this module needs to create the necessary bindings for the @Inject annotation to work properly, for example:

public class GuiceExampleModule implements Module {

  @Override
  public void configure(Binder binder) {
    binder.bind(ISingleton.class).to(ExampleSingleton.class)
        .in(Singleton.class);
  }

}

With this new attribute, using TestNG with Guice has never been easier. Try it for yourself, download the beta and tell us what you think!