Currently, you can install multiple versions of the same gem just fine:
```
$ gem install simplecov:0.19.0 simplecov:0.22.0
Fetching simplecov-0.19.0.gem
Successfully installed simplecov-0.19.0
Parsing documentation for simplecov-0.19.0
Installing ri documentation for simplecov-0.19.0
Done installing documentation for simplecov after 0 seconds
Fetching simplecov-0.22.0.gem
Successfully installed simplecov-0.22.0
Parsing documentation for simplecov-0.22.0
Installing ri documentation for simplecov-0.22.0
Done installing documentation for simplecov after 0 seconds
2 gems installed
```
But to uninstall both of them, you need to run the equivalent uninstall
command twice:
```
~$ gem uninstall simplecov:0.19.0 simplecov:0.22.0
Successfully uninstalled simplecov-0.22.0
~$ gem uninstall simplecov:0.19.0 simplecov:0.22.0
Gem 'simplecov' is not installed
Successfully uninstalled simplecov-0.19.0
```
This resolves that problem by using the gem's full name (which includes
the version) when tracking which ones have already been uninstalled so
when it gets to the second version listed it doesn't think it was
already uninstalled.
https://github.com/rubygems/rubygems/commit/d96101b753