In trying to deploy my application to Heroku, I discovered that my Ruby SDK and related code were out of date from Heroku's perspective, so I updated. At some point (I actually don't know when), RubyMine lost track of the code as a project. By this I mean that from one hour to the next, after merging in code from Git to resolve a fast-forward conflict, I tried to run the test suite, and received the error "No Gemfile found". Which is odd, because there's one I can see and open in the root of the directory pointed to by the "Project Files" tool.
Indicative of this is the fact that the entire "Project Files" tree is against a cream-colored background (as opposed to the normal white).
If there's any further information I can supply that would be useful, please don't hesitate to point that out.