Taming Legacy APIs with Snapshot Testing

Legacy APIs are a fact of life in most organizations. They may lack clear documentation, have grown organically over years, or depend on systems that few people fully understand. Refactoring them, or even changing a single field, can feel like walking a tightrope. The risk of breaking existing consumers, internal or external, is real, and the cost of comprehensive manual testing often makes teams hesitate to touch the code at all. Snapshot testing offers a practical way to bring legacy APIs under control without rewriting the world. The Legacy API Problem Legacy APIs tend to share a few traits: inconsistent response shapes, undocumented side effects, and a long history of "it works" that nobody wants to disturb. Writing traditional assertions for every endpoint means either maintaining enormous test suites or accepting partial coverage. Many teams settle for the latter. They assert status codes and perhaps a handful of critical fields, leaving the rest of the response unverified. That