Heroku could not detect rake tasks (LoadError: cannot load such file -- rspec/core/rake_task)

If rspec isn't in the production group (it generally isn't) then the code you posted would fail when run in a production environment like heroku.

In the rspec docs they recommend doing this:

begin
  require 'rspec/core/rake_task'
  RSpec::Core::RakeTask.new(:spec)
rescue LoadError
end

So that the absence of rspec doesn't stop your rakefile loading.

FWIW, I just faced the same issue. I fixed it by moving rspec-rails to production as shown below. I don't know why it works, but it works for me.

group :production, :development, :test do
  gem 'rspec-rails', '~> 3.8'
end

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