I have a plugin that uses RSpec, and it’s being used by a Rails app that
does not otherwise use RSpec (and does not want to).
I can install the RSpec gem, but of course there is no RSpec-on-Rails
gem. And I wouldn’t really want to include the whole rspec-on-rails
plugin inside my plugin, even if such a thing would work. Yet it would
be nice if the app’s continuous integration server could run specs
against all its plugins.