Im currently developing a Atom Test Coverage package for atom that depends on simplecov but will also support other frameworks later.
With this package you will always see your current test coverage in the statusbar and a detailed view when you click on the statusicon or press cmd+alt+c. The Views will refresh right after the test coverage.json file has reloaded. So if you are running your tests via guard, it will be automatically refreshed after every change.
I would be really happy if some ruby developers that are using testing frameworks (i hope all of you do) to install the simplecov gem and test it out a little bit
GitHub Repository: https://github.com/philipgiuliani/coverage