Inject different implementation for testing

Question

I have the following classes:

public interface Emailer {}

@Named    
public class RealEmailer implements Emailer {}

@Named
public class NoOpEmailer implements Emailer {}

And my service class uses the real emailer:

public class SomeService {
    @Inject
    private Emailer emailer;
}

The question is, in my service test class (SomeServiceTest), how do I inject the Emailer in the service to use NoOpEmailer ? I'm using Spring for the DI framework.

Answer 1

If you can use Spring 3.1 you can use Profiles. This would allow you to provide two different implementations of the same bean (Emailer and NoOpEmailer). Then in your test you can use the @Profile("test") annotation to activate the test profile and your no op bean will be injected.

Answer 2

Have you considered the possibility of making the field package scope rather then private as this would make it a lot simpler to set this field during your unit test (assuming your test class is in the same package as your subject).

If not, it seems to do this with Spring you would use ReflectionTestUtils#setField(Object target, String name, Object value) to inject this value into your class