ruby-on-rails - Rails/Rspec: 初期化されていない定数 Rails (NameError)

Question

実行するbundle exec rake specと、このエラーが発生し続けます。uninitialized constant Rails (NameError)

ここに私の宝石ファイルがあります:

group :development do
  gem 'guard-rspec'
  gem 'guard-spork'
end

group :development, :test  do
  gem "debugger-ruby_core_source", "~> 1.2.2"
  gem 'debugger' 
  gem 'faker'
  gem 'rspec-rails' 
  gem 'factory_girl_rails'
  gem 'spork-rails', "~> 3.2"
  gem "database_cleaner", "~> 0.9"
end

group :test do
  gem 'capybara' 
  gem 'guard-rspec' 
  gem 'launchy'
  gem "shoulda-matchers", "~> 2.0"
  gem "selenium-webdriver"
  gem "rspec-sidekiq"
end

なぜこれが起こっているのか理解できません...