Object Mentor Blog: So... You want your code to be maintainable.

So... You want your code to be maintainable.

Uncle Bob — Tue, 24 Jun 2008 23:07:46 -0500

We know that maintenance is 90% of the software lifecycle, and 90% of the cost. We know that our systems need to be flexible, reusable, and maintainable. Indeed, that’s why we spend so much of our time trying to get the design and architecture just right. Because we all know that good design and architecture is the key to flexibility, reusability, and maintainability…right?

Of course. Good design and architecture is what makes software easy to change. Good design and architecture separates the things that change for one reason from the things that change for another reason (The Single Responsibility Principle). Good design allows us to add new features without changing a lot of old code (Open Closed Principle). Good design makes sure that high level policy does not depend on low level detail (Dependency Inversion Principle), etc. etc.

So how do we get good design? Well, that’s tricky. Oh it’s not too tricky to get a good design in place at first. The tricky part is to keep the design good. That’s the problem, you see. It’s not that the design starts out so bad (although sometimes…) rather it is that the design degrades over time as the system changes.

Systems change. Often they change in ways that thwart the original intent of the design. Unfortunately, changing the design to align to these changes is hard. So we wind up hacking the new features into the system and thwarting the design. And that’s how even the best designed systems rot.

So how do we keep the design from rotting? How do we make sure we can migrate the design as the system changes? Simple. Tests.

When you have a suite of tests that covers >90% of the code in the system, you are not afraid to make changes. Every time you make a little change you run those tests, and you know that you have not broken anything. This gives you the confidence to make the next change, and the next, and the next. It gives you the confidence to change the design!

Nothing makes a system more flexible than a suite of tests. Nothing. Good architecture and design are important; but the affect of a robust suite of tests is an order of magnitude greater. It’s so much greater because those tests enable you to improve the design.

This can’t be overstated. If you want your systems to be flexible, write tests. If you want your systems to be reusable, write tests. If you want your systems to be maintainable, write tests.

And write your tests using the Three Laws of TDD.

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Sat, 28 Jun 2008 10:35:38 -0500

Although I agree with the start (about design) and the finish (about tests), I don’t think tests enforce your design. They just check that your system works correctly. For example, I can have 90% test coverage and still make direct database calls in my view. This is bad design and good tests.

"So... You want your code to be maintainable." by Rich Sharpe

Thu, 26 Jun 2008 14:26:00 -0500

“The tricky part is to keep the design good”

Although I agree this is difficult a large part is Attitude! Both you and Scott Bain, in his book Emergent Design, discuss evolving the Professionalism of our industry. If a developer has the attitude of ‘every time I touch the code, I will make it a bit better’ then they are on the path to keep the design good.

Of course we do not live in a Utopia and some developers just want to hack code for the pay…and obviously ‘a bit better’ is subjective – but I think you get the point ;-)