While unit tests are valuable for regression testing, a test harness that supports progression testing is at least as useful. Agile development methodologies tend to focus on the idea of iterating continuously toward a goal along a known path; but what happens when there’s a fork in the road? Is it up to the architect to choose a path? There’s no reason to do so when you can take both roads and decide afterward which you prefer.
Write it, demo it, document what you’ve learned, and then throw the code away. Then you can write the real thing.
It may seem like a waste of time and effort at first. You’ll be tempted to over-engineer, you’ll be tempted to refactor, you’ll be tempted to keep some or all of the code. Resist the urge.
Why would you do such a thing? If you’re practicing agile development, you might think your regular development is fast enough that you don’t need a proof. But that’s not the point; the point is to learn as much as you can about what you’re proposing to do before you go all-in and build an architecture that doesn’t fit and that will be a pain to refactor later.
Even if it takes you longer to build the proof,it’s still worth it – for one thing, it probably took longer because of the learning curve and mistakes made along the way that can be avoided in the final version, and second because again, you’ve learned what you really need and how the architecture should work so that when you make the production version you can do it right the first time, with greater awareness of the situation.
This approach allows much greater confidence in the solutions chosen, requiring less abstraction to be built in to the application, which allows for leaner, cleaner code, and in less time. Add to that the value of building a framework that is flexible enough to allow for progression testing, and you’ve got the kind of flexibility that Agile is really all about.
Note: Yes, I understand that Scrum calls prototypes “spikes”. I think this is rather silly – there are already terms for prototypes, namely, “prototype” or “proof of concept”. I’m all for new terms for things that don’t have names, but giving new names to things that already have well-known names just seems unnecessary.