standalone_controller.rb

require 'rubygems'
require 'action_controller'

class StandaloneController < ActionController::Base
  def index
    render :text => 'Hello'
  end
end

# blows up without session config otherwise
ActionController::Base.session_store = nil

# usually looks for controllers in app/controllers/**
ActionController::Routing.use_controllers!(['standalone'])
ActionController::Routing::Routes.load_routes!
dispatcher = ActionController::Dispatcher.new

env = Rack::MockRequest.env_for('/standalone/index')
status, headers, body = dispatcher.call(env).to_a

puts "HTTP #{status}"
body.each do |part|
  print part
end
puts