Rails upgrade's best friend

By comparing all these HTML files that are processed before and after any kind of code change, you can make sure that you did not (or you did) introduce any new user-facing incompatibilities. This may greatly help you for example, refactoring your app, replacing external libraries, or upgrading libraries. My personal use case that made me gemifying still_life was that I wanted to make sure that my own template engine renders the same HTML as the one that I was using.But indeed, the real sweet spot of this tiny library is IMO "Rails upgrade". In fact, The first original version of this tool was implemented as an RSpec monkeypatch while we were upgrading a huge Rails application from Rails 2 to Rails 3.