When TDD Is Not The Hammer

Not Hammer Time
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I always tell people: When you need to add a new feature, use the TDD way. Write a test first, make small steps, and all will be well.

But sometimes, we need to take other paths.

I was working on a new feature last week. I already had a test in place, and a couple more to follow. I usually write those in comments, so I won’t forget to make sure they work, or add the code.

And so I start coding. And move code around. And refactor here and there. And low and behold, after two hours, I’m still in the same place. That test still doesn’t pass. I took a step back, slept on it, and reverted to the original passing code.

Job too big for one test

I knew where I was going (better than when I started the first time). So while all tests were green, I started to refactor the code, putting placeholders for the new code. This is similar to coding by intention, or a variant of “fake it till you make it”.

Then I went to the test side. I thought about going with TDD for a more internal component, but the way the architecture was built, it didn’t make sense to me. Plus, the original test described the behavior I wanted. I kept the original test.

Next, I went back to the code. I had some placeholders to fill. I knew that some of the code will converge into the same methods. But I was careful not to touch the existing code. I only added code,  duplicated (sometimes triplicated) it. I knew that there will be time for refactoring when everything works. I kept running the tests to make sure the old tests still work.

After an hour or so, I had most of the code in place, and still, a failing test. Just filling the placeholders was not enough. I could have reset and start over. But I decided to push through. Half an hour later the test was passing. A few minutes later the additional tests were passing, without adding more code. An hour later, the code was refactored to my satisfaction.

What lessons can we learn?

  • TDD tells us to go in small steps. That is, small working increments of code. But sometimes the jump is too big. Real life is hard.
  • Doing a once-over, even if not completed, did help. It showed me the “design of things to come”.
  • Throwing away the changes helped, and didn’t feel wasteful. I was no longer bound to my changes from the first session.
  • Working without a net (while not all tests are passing) felt weird (even scary). Going in the second time, I already knew it won’t be easy. But having the placeholders helped me feel I’m on the right path, as I was making them green.
  • Knowing there’s going to be refactoring later also helped. I concentrated on “making it work”, rather than the nagging “how it looks” feeling. I did fight the urge to consolidate code that looked similar, but prevailed.
  • At the end I was happy. The feature worked, I had passing tests, and the code looked better (although not exactly as I envisioned).

So what is the moral of the story? TDD is still my favorite way of coding. But like every tool, it’s not the only one I can use. In reality, It’s not the hammer for every nail out there.

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