title: Install a specific set of gems in a CircleCI configuration file
body: <p>I am trying to build a CircleCI configuration file that only installs a specific set of gems via the environment parameter.  In this case let's call that environment <code>continuous_integration</code> and this environment matches the <code>test</code> environment.  So far I have tried a number of things and this is my current configuration in this spike.  </p>
  
  <p>Could anyone point me in the right direction? Is this possible?</p>
  
  <pre><code>machine:
    timezone:
      America/Los_Angeles
    ruby:
      version:
        2.4.1
    services:
      - redis
    environment:
      RAILS_ENV: continous_integration
  
  database:
    override:
      - bundle exec RAILS_ENV=continous_integration rake db:drop
      - bundle exec RAILS_ENV=continous_integration rake db:setup
  
  dependencies:
    pre:
      - gem install bundler
    override:
      - bundle install:
          timeout: 180
          environment:
            RAILS_ENV: continous_integration
  
  test:
    override:
      - bundle exec RAILS_ENV=continous_integration rspec 
  </code></pre>