Coffeescript building with Rake and Jasmine testing with capybara

Rakefile

# This is a pure rake-style build process for building coffeescript files to js
# using the coffee-script ruby gem and Rake's `rule` and `file` directives.
# That means that a js file will only be built if it is out of date.

require 'rubygems'
require 'bundler/setup'
require 'coffee-script'
require 'capybara-jasmine'
require 'capybara/poltergeist'
require 'rake/clean'

# This says "to make a js file, find a coffee file of the same path
# then run this task"
rule '.js' => '.coffee' do |t|
  puts "Compiling #{t.source} => #{t.name}"
  File.write(t.name, CoffeeScript.compile(File.read(t.source)))
end

# `rake clean` removes these files
CLEAN.include "app/**/*.js"
CLEAN.include "spec/**/*.js"

# Find all the coffee files, change ext to js
# and for each one, make the coffee task depend
# on the js file
FileList['**/*.coffee'].ext('js').each do |f|
  task :coffee => f
end

# At this point `coffee` depends on stuff like `path/foo.js`
# which will be built by compiling `path/foo.coffee`

# Now, use Capybara::Jasmine to make a `spec` task
# It depends on `coffee` which is the union of all
# the compiled js
Capybara::Jasmine::TestTask.new "spec" => "coffee" do |t|
  # let's use phantom!
  Capybara.javascript_driver = :poltergeist

  # order-dependent lib files
  t.lib_files = FileList[
    "vendor/jquery-1.8.2.js",
    "vendor/underscore.js",
    "vendor/backbone.js",
    "app/mb.js",
    "app/**/*.js" # then the rest
  ].uniq # don't duplicate mb.js or others, they'd get overwritten
  t.spec_files = FileList["spec/**/*Spec.js"]
end

task :test => ['coffee', 'spec']
task :default => :test