Working on an existing code base that has minimal or no tests is like walking on eggshells: Every move you make has the potential to break something. Yet when you're working on software, the damage is not always immediately obvious—at least, not without extensive, system-wide testing. But such validation is not always possible or easy, considering the frequency of change, limited resources, and looming deadlines that most developers face. As a result, many developers commit their additions and modifications, then cross their fingers and hope for the best.
If your code lacks sufficient tests, Behavioral Regression Testing is a technique that provides a fast and easy way to determine if code modifications change or break existing functionality. What is Behavioral Regression Testing? It's a baseline test that captures the project code's current functionality. To detect changes from this baseline, you run your evolving code base against a test suite on a regular basis. In most cases, such a test suite can be generated overnight using automated unit-testing tools. Once this test suite is in place, you can incrementally improve its intelligence and value by adding more test cases, modifying the automatically generated ones, and keeping it in sync with intentional program changes. The resulting test suite serves as a change-detection safety net, letting you modify code without fear of accidentally changing or breaking the code's intended behavior.
The key to making this practice practical is to automate as many tasks as possible so that you can focus your efforts on the few regression-testing tasks that truly require human intelligence. By leveraging automation for this purpose, you gain a reliable way to determine when and how your code modifications impact the rest of the application—with minimal effort.
In this article, I explain how to build, maintain, and extend Behavioral Regression Test Suites that help you write code faster and change it with confidence.
