processing is turn off for sake of test speed

# spec/my_test.spec
before do
  DocumentUploader.enable_processing = true
end

It’s probably because you have something like

# config/initializers/carrierwave.rb
if Rails.env.test?
  CarrierWave.configure do |config|
    config.storage = :file
    config.enable_processing = false
  end
else
  CarrierWave.configure do |config|
    config.storage = :fog
  end
end

I recommend to keep the enable_processing = false and just overide it when needed