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The difference between Test First and Test Driven Development


The concept of Test First (“TF”, write a failing test first and make it green by writing exactly enough production code to do so) was always very appealing to me. But I’ve never experienced the guiding effect that is described for Test Driven Development (“TDD”, apply a Test First approach to a problem using baby steps, letting the tests drive the production code). This lead to quite some frustration and scepticism on my side. After a lot of attempts and training sessions with experienced TDD practioners, I concluded that while I grasped Test First and could apply it to everyday tasks, I wouldn’t be able to incorporate TDD into my process toolbox. My biggest grievance was that I couldn’t even tell why TDD failed for me.

The bad news is that TDD still lies outside my normal toolbox. The good news is that I can pinpoint a specific area where I need training in order to learn TDD properly. This blog post is the story about my revelation. I hope that you can gather some ideas for your own progress, implied that you’re no TDD master, too. A simple training session

In order to learn TDD, I always look for fitting problems to apply it to. While developing a repository difference tracker, the Diffibrillator, there was a neat little task to order the entries of several lists of commits into a single, chronologically ordered list. I delayed the implementation of the needed algorithm for a TDD session in a relaxed environment. My mind began to spawn background processes about possible solutions. When I finally had a chance to start my session, one solution had already crystallized in my imagination:
An elegant solution

Given several input lists of commits, now used as queues, and one result list that is initially empty, repeat the following step until no more commits are pending in any input queue: Compare the head commits of all input queues by their commit date and remove the oldest one, adding it to the result list. I nick-named this approach the “PEZ algorithm” because each commit list acts like the old PEZ candy dispensers of my childhood, always giving out the topmost sherbet shred when asked for.

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The difference between Test First and Test Driven Development