Behaviour Driven Development for Ruby
rspec is a meta-gem, which depends on the rspec-core, rspec-expectations and rspec-mocks gems. Each of these can be installed separately and activated in isolation with the gem command.
Conversely, if you like RSpec's approach to declaring example groups and examples (describe and it) but prefer Test::Unit assertions and mocha, rr or flexmock for mocking, you'll be able to do that without having to load the
components of rspec that you're not using.
gem install rspec