Diffblue Cover should provide meaningful stubs for object dependencies

1

In OOP, testing classes often involves stubbing the dependencies.

A common example is that of Service / DAO (Data access object) pattern:

Consider the implementation of FruitService below:

public class FruitServiceImpl implements FruitService {

    private final FruitRepository fruitRepository;

    public FruitServiceImpl(FruitRepository fruitRepository) {
        this.fruitRepository = fruitRepository;
    }

    @Override
    public List<Fruit> getFruitsInStock() {
        return fruitRepository.getAllFruits().stream()
                .filter(fruit -> fruit.getQtyInStock() > 0)
                .collect(Collectors.toList());
    }
}

Testing the “getFruitsInStock” method would mean asserting that only fruits whose qtyInStock > 0 is returned.

Logically, this can be tested without any concrete implementation of FruitRepository being provided.

However, DiffBlue cover fails to generate a test for this method stating:

Cannot generate essential test for getFruitsInStock: Unable to generate test inputs not throwing a trivial exception. 
Diffblue Cover could not determine valid inputs for the methods under test.

I think the tool should be able to generate meaningful stubs where possible. Is this a known limitation or am I missing something ?

2

Thanks for your concise example – short answer is yes, it is a known limitation of the current product and we have been thinking about how to solve for this and similar cases.

3

I’m sorry but this makes DiffBlue Cover totally unusable in real world scenarios. If DiffBlue is not dependency injection aware, how can it ever generate any meaningful tests?

I paid for a subscription and ran it on a spring boot (spring batch) application and for 99% of the methods that I tried to generate a test for it gave me the error referenced above.

4

@pojomojo, if you use Spring Boot and use @Autowired for injecting dependencies into your components then Cover creates tests that inject these dependencies using @MockBean. This works for Repositories as well as Services and other Components that your Services and Controllers depend on.