BUNDLE_GEMFILE=Gemfile bundle install && bundle exec rake spec
BUNDLE_GEMFILE=Gemfile.mongoid-two bundle install && bundle exec rake spec
BUNDLE_GEMFILE=Gemfile.mongoid-three bundle install && bundle exec rake spec
BUNDLE_GEMFILE=Gemfile.mongoid-four bundle install && bundle exec rake spec

Add shell script that runs tests for each Gemfile
Add shell script that runs tests for each Gemfile
