Luca Minudel commented on my previous post. My answer has got so long that it became a full post.
I’m a fan of the Growing Object-Oriented Software book, but I haven’t adopted the mockist style yet. I know that I have seen lots of instances of mock misuse, leading to unreadable and brittle tests. So I’m afraid it depends a lot on who’s doing the training :-) It’s true that the GOOS book promotes good object-orientation.
My point in my previous post was not advocating a particular style of training. It is simply to answer a common question. “If we work incrementally without design upfront, as all the books on TDD advocate, is there a risk of getting in a situation where adding some features becomes unreasonably expensive?” This fear is often related to non-functional requirements.
I think this fear has merit, and it’s too easy for new converts to TDD (including me) to confidently say “we have the tests, we can refactor the code to make it do whatever is needed.” The bug in this reasoning is that we should not code with the expectation to do (what often amounts to) major refactoring. We should code with the objective of producing a system where implementing new stuff is so easy that it feels like composing Lego bricks, or like putting the last piece of a puzzle, when it slides comfortably in its place.
Getting to a design that is this good is the real goal of TDD and XP. I can’t say in all honesty that I can achieve this level of goodness in major applications. But I’m beginning to see how one could do that.
So the point of my post is that you can afford to work in a totally incremental way, only if you are dead serious about keeping your code squeaky clean. Which is not easy to do, given the time pressures we always have. But then again, this is nothing new, this is what the XP books have been saying from the beginning, isn’t it? Only it is surprising to discover how really clean your code should be.
Coming back to your comment, it seems you are concerned with ways to help a team to do the right thing and produce good code. My experience is that the first step is to know your material well. So if you’re accomplished producing good code in the mockist style, more power to you! Your team will pick it up from you.
It’s interesting that you found it easier to communicate good style using the mockist approach rather than teaching principles like OCP and Demeter. I’ll have to think about it.
Dear reader: if you haven’t read Growing Object-Oriented Software yet, I invite you to do so. It’s not a book about “mocks” simply. It’s a book about a style of software development, deeply and beautifully object-oriented. For a taste of the authors’ style, I suggest you to read their paper Mock Roles, Not Objects (pdf).