I’ve recently been working on adding a new feature that, for many reasons, requires a great deal of refactoring to our existing codebase.<\/p>\n\n\n\n
I’ve done code refactoring for most of my career, and I’ll do it many more times until the day I retire. When I started, though, things were a bit different from what they are now. I didn’t know about the concept of unit testing, and the companies I worked for were not interested in or didn’t know about this concept either. As a result, I relied on manual verification tests to confirm that everything was fine. Many times they were not, and I would just find my bugs when they were already in production.<\/p>\n\n\n\n
The introduction of automated testing, particularly unit and integration tests, was a game changer. Many time, when I write a new feature, it takes me way more time to write automated tests than to write the actual code for the feature! But despite this, I keep writing them every time because I know how useful they are.<\/p>\n\n\n\n
When we already have automated tests for a feature, doing a refactor is usually as simple as just changing the code, and running the tests. That only works if we already have a good test coverage though.<\/p>\n\n\n\n
The area that I am touching has an uneven test coverage, so, before refactoring the code, I need to write the missing tests so I can validate how the feature works. A few times I have even found bugs in production code by doing this. Only once I have improved the test coverage I move to changing the code.<\/p>\n\n\n\n
It’s important to remember that automated tests are not perfect. They cannot test every scenario, and we’ll likely forget to add some (I’ve been guilty of this a few times during this refactor). As Dijkstra said [1]:<\/p>\n\n\n\n
\nProgram testing can be used to show the presence of bugs, but never to show their absence!<\/p>\n<\/blockquote>\n\n\n\n
But even considering that, aiming for a high coverage that follows a good test design gives us way more confidence than having no tests at all.<\/p>\n\n\n\n
Happy coding!
Jos\u00e9 Miguel<\/p>\n\n\n\nShare if you find this content useful, and Follow me on LinkedIn<\/a> to be notified of new articles.<\/em><\/p>\n\n\n\n