[crdoconnor]

>Outside-in and promiscuous mocking has several advantages -- especially when you are less experienced. It provides a framework for reasoning about how to do design.

I find that any additional couplings to your code makes the couplings you do have more painful to work with.

Some people think that by adding this kind of 'tight coupling' - low level mocks / unit tests - you feel that pain earlier on in the design process and that pain drives you to make a better, more loosely coupled code design.

Personally, I think that this approach is rather like forcing kids to smoke cigarettes every day to show them how much of a filthy dirty habit it is.

[mikekchar]

Very similar to cigarettes, the really nasty effects don't usually materialise until quite far down the road -- when you don't have much opportunity to deal with them.

However, I don't think it has to be like this. I sometimes call mocking "wish based design". Sometimes you don't really know what shape is going to be good. You know ahead of time that TDDing a solution is likely to churn a lot of time writing stuff you are going to ultimately throw away. You can spike a solution to get some more information, but there is often a lot of pressure to ship whatever you spiked, no matter how successful you were (or how bad your tests ended up being).

With a mocking approach you think to yourself, "If this were already written and I was using it, ideally how would it work?" You mock your wish and you write the use side of the code in your tests. Quite frequently this reveals most of your naivety and allows you to design what it is you need. At that point, you replace the mocks with real implementation. It's at this point where I differ from the main proponents of the style (or at least last time I talked to them, which is admittedly several years ago). I will TDD my implementation, removing the mocks as I go.

So, on reflection, I guess I use it in places where I would otherwise spike a solution. Again, for fairly junior people, it can be a great technique to help them understand where to start. Often I find that junior people can't do TDD because they simply can't envision what they are building. They will spike a solution, jam a couple of tests in to show that it's basically working and call it a day. A mocked solution often ends up exposing state in the places where it needs to be. This is frequently better than the spiked solution which is usually an encapsulated ball of mud.

As I said before, though, I use it as a technique of last resort, not a technique of first resort.

[crdoconnor]

>However, I don't think it has to be like this. I sometimes call mocking "wish based design". Sometimes you don't really know what shape is going to be good.

That's why I write executable specs at a high level with my "wish based design", make that "test" pass and then refactor. Wish first -> code next -> only well designed code after that.

I don't feel the need to dive down another level and mock out real modules that are already covered by this high level test. That's just creating unnecessary work for myself and introducing a potential source of test bugs (where the mock doesn't match the reality).