As your application grows, so does the risk of breaking existing features. Regressions are the silent killers of user retention. Here is how to build a defense system that evolves with your codebase.

"The only thing worse than a bug is a bug you've already fixed coming back."

1. Visual Regression Testing

Pixel-perfect UIs are hard to maintain. We use tools like Percy or Chromatic to automatically detect visual changes in every build. If a button padding shifts by 2px, we know about it before the user does.

2. Contract Testing

In microservices, breaking API changes causes downstream chaos. We implement Consumer-Driven Contracts (Pact) to ensure that services communicate correctly. If the API changes its contract, the consumer tests fail immediately.

3. Database State Management

Data regressions happen when schema changes break application logic. We treat database migrations as code, with roll-forward and roll-back tests integrated into the deployment pipeline.

Scale introduces complexity, but it doesn't have to introduce chaos. With the right regression guards, you can scale safely.