Comments on: Tell, Don’t Ask – Part 2

By: Colin Jack

Colin Jack — Sun, 06 Sep 2009 16:44:10 +0000

@ketan
I think you are missing Brians point, he is saying your unmocked test is not realistic and provides a better example. Its not that he doesn’t understand that mocking allows you to replace dependencies

I’d also argue that it is worth focussing on the key advantages of mocking. It isn’t just about making it easier to test, its about pushing forward your design. See mockobjects.com or “Mock Roles, Not Objects”.

Having said that to me mocking domain objects, like dog/owner here, is often a mistak. I might well use state based testing in this sort of situation even if keeping PetOwner/Dog very loosely coupled is important, but thats a seperate discussion.

By: Ketan

Ketan — Fri, 04 Sep 2009 21:36:53 +0000

@Brian,

With a mock dog, the owner need not have a real dog to feed to test if the owner can actually perform an operation.

By: Ketan

Ketan — Fri, 04 Sep 2009 19:43:56 +0000

@Nick,

Thanks for catching this. The example is supposed to be using constructor based injection. I’ve updated the post accordingly.

By: Brian Swan

Brian Swan — Fri, 04 Sep 2009 08:54:33 +0000

I’m not a big fan of Mocks but the non mocked example test seems overly contrived. There is no reason to not use constructor injection in the first example or to have a Dog class that needs two phase construction. From Tell, Don’t Ask – Part 1 we know that the Dog has an isHungry query method, so I would have written the following test with no need for mocking.

void testOwnerCanFeedDog(){
Dog dog = new Dog();
PetOwner owner = new PetOwner(dog);
owner.feedDog(food);

assertFalse(dog.isHungry())
}

By: Nick Stolwijk

Nick Stolwijk — Fri, 04 Sep 2009 06:14:59 +0000

In your second test, how does the PetOwner know of the mocked Dog?