Why is Heroku installing rspec?

This is what I have in my Gemfile:

sour开发者_开发百科ce 'http://rubygems.org'

gem 'rails', '3.0.5'
gem 'sqlite3'
gem 'hoptoad_notifier', '= 2.4.2'

group :development, :test do
  gem 'ruby-debug'
  gem "factory_girl_rails"
  gem "database_cleaner"
  gem "rspec-rails"
  gem "cucumber-rails"
  gem "capybara"
  gem "launchy"
  gem "redgreen"
  gem "faker"
  gem "remarkable_activerecord"
end

When I do

git push heroku master

on my screen this is what I see

Installing rspec-core (2.5.1) 
Installing rspec-expectations (2.5.0) 
Installing rspec-mocks (2.5.0) 
Installing rspec (2.5.0) 

I thought Heroku installs in production mode, then why rspec is being installed?

That's because by default all groups are installed. To tell Heroku to ignore certain groups, run

heroku config:add BUNDLE_WITHOUT="development:test"

You can read more about using Bundler with Heroku if you wish.