Whenever I talk to someone who is interested in learning TDD I let them know that it is a very difficult concept to put into practice. It takes a lot of discipline and significant changes in the way you think and code.
Nobody mentioned this to me before I started. Everyone spoke of TDD like magic -- it changes your design, its the best thing ever, its so simple, all you need to do is write your tests before your class, you'll love it... (Ignore the man behind the curtain!)
After a few days of trying, I began to think something was very wrong. I wasn't quite the developing genius I thought...
That couldn't be true!
Like any reasonable person in my situation -- overstressed, too many responsibilities, tight deadlines, stakeholders bothering you, etc... I continued to pound my head against what seemed to be a steel wall of TDD that just wouldn't fit.
My head (now bleeding and bruised) was focused on how to solve the problem instead of how to test the solution. I didn't know it at the time, but until I changed this behavior, I would always be fighting my instincts and not gaining the benefits.
Fast forward two months and I was still, well, sucking, but not as bad. I had some test coverage, I wrote some classes test first, but I did not test drive every class, it seemed like too much work. I also didn't understand mocks, at all, and gave up on writing my own mock classes after about a day, so no interaction testing and lots of coupling.
It was very frustrating to have 1/3 of my tests fail if I was working on a common entity or if a bug showed up. Also, because I was coupling all my classes together I wasn't seeing the full benefits of test driving.
My focus was just as bad as coding before. If I needed a new behavior, I'd have to code. This meant testing the other class, which may cascade into other tests. Thinking about it, I think my focus was worse. Sometimes I could write a stub for the new behavior, but say I was creating a method that returned a boolean that had different responses that I needed to test... And there is the setup to get it into each state. And thats just a boolean assuming there's no interactions...
My thinking was in the same place it was a few months earlier. The only difference was I could write a unit test before I wrote code. But I wasn't test driving design. I had the design in my head. I was writing the unit tests for the classes and interactions I already decided I needed.
Fast forward two months: New job, new project, fresh start, woo hoo!
With this project, I was determined to understand TDD. A lot of bright people that I respected were saying great stuff and I was going to get it.
My first step was to understand nMock.
I knew using real classes in my tests was killing my focus, but I didn't yet know how much it affected my design. I read the nMock web page, explaining the api, about 500 times... "Okay," I said to myself. "You can use an interface before its implemented and verify its been called."
It sounded so simple, it read so simple, yet it made NO sense to me.
My delight in using mocks (once I figured out how to use them) was focused on several things -- I could focus on the test I was writing, my tests weren't failing because of another class and my tests were a lot simpler because I didn't need to put in knowledge about other classes to verify or assert behavior in the CUT. Implementations of interfaces used in tests didn't affect the tests anymore.
After a few weeks of nMock, what I began to notice was that my design, code, thinking, and mind was changing.
I only made a class after it was being used as an interface in another class. That class' only public methods were in that interface. I never debugged my application. I almost never debugged my tests. My test coverage was over 90%. My design evolved through the tests.
I was test driving. Finally!
Making tests was so focused and had immediate results I was addicted. At some point, something happened in my brain and this great thing called TDD finally came in. I didn't want to write in the CUT first, because it wasn't how I was thinking. It seemed like more work.
I was in the test.