[#2180] Low-level Carrierwave to ActiveStorage migration

spec/services/carrierwave_active_storage_migration_service_spec.rb

@@ -0,0 +1,9 @@
+require 'spec_helper'
+
+describe CarrierwaveActiveStorageMigrationService do
+  describe '#hex_to_base64' do
+    let(:service) { CarrierwaveActiveStorageMigrationService.new }
+
+    it { expect(service.hex_to_base64('deadbeef')).to eq('3q2+7w==') }
+  end
+end