Debugging and testing go hand-in-hand. But how can you write unit tests for a legacy application? Most of the time, there *are* no “units” in a legacy application. Everything is tied to everything else, so testing anything in isolation is impossible. However, you don’t have to use *unit* testing to discover bugs when you make changes. You can use *characterization* testing instead. In this presentation, Paul will talk about what characterization testing is, how to apply it, and how it can help you to manage and maintain legacy applications, especially while refactoring and modernizing.