// ...
public interface GenericInterface<T> {
    void genericArg(@NotNull T arg);
    void stringArg(@NotNull String arg);
}

public interface StringInterface extends GenericInterface<String> {
}

// ...
@ValidateOnExecution(type = ExecutableType.ALL)
public class StringImpl implements StringInterface {

    @Override
    public void genericArg(@NotNull String arg) {

    }

    @Override
    public void stringArg(@NotNull String arg) {

    }
}

// ...
@RunWith(Arquillian.class)
public class ValidatorTest {

    @Deployment
    public static WebArchive deployment() {
        return ShrinkWrap.create(WebArchive.class)
                .addAsWebInfResource(EmptyAsset.INSTANCE, "beans.xml")
                .addPackage(ValidatorTest.class.getPackage());

    }

    @Inject
    private StringInterface bean;

    @Test(expected = Exception.class)
    public void validation_on_generic_arg(){
        bean.genericArg(null);
    }

    @Test(expected = Exception.class)
    public void validation_on_string_arg(){
        bean.stringArg(null);
    }
}