diff --git a/app/mailers/base_mailer.rb b/app/mailers/base_mailer.rb
index 49a2ebc5d..353ba556c 100644
--- a/app/mailers/base_mailer.rb
+++ b/app/mailers/base_mailer.rb
@@ -1,5 +1,8 @@
+# frozen_string_literal: true
+
+# Mailer configuration
 class BaseMailer < ActionMailer::Base
-  default :from => ENV['DEFAULT_MAIL_FROM']
+  default from: ENV['DEFAULT_MAIL_FROM']
   layout 'notifications_mailer'
 
   helper :application
diff --git a/config/initializers/sidekiq.rb b/config/initializers/sidekiq.rb
index 180690249..dfb92c5d4 100644
--- a/config/initializers/sidekiq.rb
+++ b/config/initializers/sidekiq.rb
@@ -1,24 +1,28 @@
-if Rails.env.staging?
-  namespace = "fablab_staging"
-else
-  namespace = "fablab"
-end
+# frozen_string_literal: true
 
-redis_host = ENV["REDIS_HOST"] || 'localhost'
+namespace = if Rails.env.staging?
+              'fablab_staging'
+            else
+              'fablab'
+            end
+
+redis_host = ENV['REDIS_HOST'] || 'localhost'
 redis_url = "redis://#{redis_host}:6379"
 
 Sidekiq.configure_server do |config|
   config.redis = { url: redis_url, namespace: namespace }
 
   # load sidekiq-cron schedule config
-  schedule_file = "config/schedule.yml"
+  schedule_file = 'config/schedule.yml'
 
-  if File.exists?(schedule_file)
+  if File.exist?(schedule_file)
     rendered_schedule_file = ERB.new(File.read(schedule_file)).result
-    Sidekiq::Cron::Job.load_from_hash YAML.load(rendered_schedule_file)
+    Sidekiq::Cron::Job.load_from_hash YAML.safe_load(rendered_schedule_file)
   end
 end
 
 Sidekiq.configure_client do |config|
   config.redis = { url: redis_url, namespace: namespace }
 end
+
+Sidekiq::Extensions.enable_delay!
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 3c7af7e67..25c8d9d66 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -92,7 +92,8 @@ class ActiveSupport::TestCase
     end
 
     if Setting.find_by(name: 'invoice_VAT-active').value == 'true'
-      vat_rate = Setting.find_by(name: 'invoice_VAT-rate').value.to_f
+      vat_service = VatHistoryService.new
+      vat_rate = vat_service.invoice_vat(invoice)
       computed_ht = sprintf('%.2f', (invoice.total / (vat_rate / 100 + 1)) / 100.0).to_f
 
       assert_equal computed_ht, ht_amount, 'Total excluding taxes rendered in the PDF file is not computed correctly'