I've spent many months upgrading legacy Rails services. One particular project was upgrading several microservices from Rails 3.1 to Rails 4. The projects made

I've spent many months upgrading legacy Rails services. One particular project was upgrading several microservices from Rails 3.1 to Rails 4. The projects made use of Rspec, Test::Unit, and Capybara. There were unit tests, integration tests, and UI tests. There were over 5000 specs in total. The project also used many gems in production to accomplish its tasks. When you are forced to uprgrade: the testing frameworks themselves, the ORM, the web framework, static asset building tools, libraries for managing file uploads, map rendering, etc, all in one go, it's nearly impossible to get it 100% right. We upgraded minor versions one by one. We read the Rails release notes and any gems that had them. Every time we bumped a Rails version we broke thousands of tests. Even after months of meticulous work we had only managed to upgrade 3 of the 4 services up to Rails 4.0, with another stuck on 3.2. Is it possible to work this way? Sure. But it's insane and costly when you let it get this bad. I've yet to work on a large Rails project on a team that outsources their upgrades where upgrading was "perfectly straight forward". It sounds like you work for a company that actually cleans house. A company like that has no need to hire OP.