Testing Carrierwave with Fog for Amazon S3

CarrierWave/Fog need a non-empty file, otherwise the url to the S3 object will be nil and can’t be tested.
Fog.mock! doesn’t work out of box. Some extra steps are needed to avoid uploading files to S3 when running tests.

First, create config/fog_credentials.yml

default:
  aws_access_key_id: 'your-aws-access-key-id'
  aws_secret_access_key: 'your-aws-secret-access-key/'
  region: 'your-aws-region'

Next, put this to your config/initializers/carrier_wave.rb

Fog.credentials_path = Rails.root.join('config/fog_credentials.yml')

fog_dir = Rails.env == 'production' ? 'production-bucket' : 'dev-bucket'

CarrierWave.configure do |config|
  config.fog_credentials = {:provider => 'AWS'}
  config.fog_directory  = fog_dir
end

Next, put this into spec/support/fog_helper.rb

Fog.mock!
Fog.credentials_path = Rails.root.join('config/fog_credentials.yml')
connection = Fog::Storage.new(:provider => 'AWS')
connection.directories.create(:key => 'dev-bucket')

Note, the :key value must match whats defined for fog_dir (dev-bucket) in carrier_wave.rb

Suppose you want to test this class:

class FileUploader < CarrierWave::Uploader::Base
  storage :fog
end

Your rspec test can be something like this:

class TestFileUploader
  mount_uploader :file, FileUploader
end

describe FileUploader do
  include FakeFS::SpecHelpers

  context 'for non-production environment' do
    it 'should upload video clip to dev-bucket on s3' do
      FakeFS.activate!
      FakeFS::File.should_receive(:chmod) #this is needed or you will get an exception
      File.open('test_file', 'w') do |f|
        f.puts('foo') # this is required or uploader_test.file.url will be nil
      end
      uploader_test = TestFileUploader.new
      uploader_test.file = File.open('test_file')
      uploader_test.save!
      uploader_test.file.url.should match /.*\/dev-bucket.*/ #test to make sure that it is not production-bucket
      FakeFS.deactivate!
    end
  end
end

Now the test is complete. It uses fakefs to generate a fake file which is non-empty. Fog will pretent to upload the file using the FileUploader under test. The upload url is the subject under test.

zlu

Testing Carrierwave with Fog for Amazon S3