Jul 24

What have version control and testing to do with each other? Well, first of all, both are common virtues in the clean code community. What you’ll find is that both virtues are important on their own ground: version control provides a safety guard in that you can roll back to prior versions if you accidently introduce problems in your code. Testing (automated unit tests) provides a safety guard, too, because you can do regression testing when you work with your code. These are both fine goals but seemingly have little to do with each other.

But in reality they do. For sake of argument, let’s take a step back and assume that you have to work in an environment of several developers where neither of these things exists. What will you likely see? What we all have seen several years ago. Commented out code blocks, redundant and often misleading or outdated comments, timestamps with comments cluttered all over the code. And frightened developers that feared each minor change because of the miriad of subtle side effects it might have, let alone major changes to core components. It’s an environment in which refactorings as welll as extensions are very hard and expensive, which results in frightened overworked developers and frustrated managers.

So, what happens when you introduce only one of those virtues? Say, we introduce version control. Now, every change gets documented, except that documenting every change requires, from the developers point of view, documentation at the wrong point. They can’t see the documented changes and the reason for these changes in the source, they see it only in the version control system — iff they add a change message with every change at all. Much more likely is that you will see commit messages such as “.” or “bug fix”, and the same old mess of timestamps, outdated comments and commented out code as before. Why is that? Because your developers are now not as frightened as they used to be (because they can now rely on the version control system to fall back to older versions), but they still have the same need to understand and document the code. And the commit log is both “too far away” from the code and “out of it’s purpose” for this task: the commit log shouldn’t document what the code is supposed to do, only when something was implemented to behave in a particular way.

This is where a development (unit) test suite comes into the picture: you document every required behaviour in tests. With every change to the code, you also update the test. As a developer, you can now look into your test suite to see what the code is supposed to do. Now developers will likely become much more confident with their changes, because they can run the tests and see what happens (hopefully next to immediately) without requiring time- and resource-consuming manual tests.

But what about documenting the changes to the code? Well, you should simply document any changes in the commit message of your version control system, because it’s now no longer necessary to keep the entire version history in mind to understand what the current code state is supposed to do. You have the tests that tell you what the code should do. The commit log now only serves the purpose of documenting what has changed over time and is no longer required to understand what the code should do. So you don’t have to keep the clutter in your code, resulting in much cleaner source code files.

Summary: Taken together, the whole of version control and testing adds up to more than a simple addition of their own values.

Posted by Holger Schauer

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