Driving The Legacy Out

Today’s episode is about persistence, patience, and the power of Test-Driven Development (TDD).

At this client in the US, where I’ve got the chance to work for almost one year, their code base had grown almost exponentially, with millions of lines of code, thousands of components tangled in tightly coupled dependencies, outdated logic, and patches on top of patches. Refactoring a small bit of this legacy required 100x reading and re-reading to try to understand what was going on.

We knew the risks: change something to improve one area but break everything else around. But we also knew that if we didn’t do anything, the system would just keep on growing and growing and the client would be unsatisfied with our services.

Building Confidence One Test at a Time

Instead of diving in headfirst or rewriting everything at once, we committed to a disciplined TDD approach. Every new feature, bug fix, or refactor religiously started with writing failing tests that defined the expected behavior. Then writing code to pass those tests. Slowly, test coverage grew, covering critical paths, edge cases, and legacy components along the way.