Fix Sidekiq mailer specs

These specs were using a code snippet copied from a GitHub issue
comment, but there are some extra subtleties if we want to be able to
use two specs that set the ActiveJob adapter to Sidekiq in the same run.
Also move this to spec metadata so we can easily reuse it elsewhere if
we need to.

The reason we need this anyway is because we can't easily set a non-test
adapter for ActiveJob in tests: either for a specific test, or
globally. (Request specs will get set back to the test adapter.)

spec/initializers/mailer_retries_spec.rb

@@ -2,22 +2,8 @@
 
 require 'spec_helper'
 
-RSpec.describe 'Mailer retries' do
-  # We need to ensure that this runs through Sidekiq to take
-  # advantage of the middleware. There is a Rails bug that means we
-  # have to do some extra steps to make this happen:
-  # https://github.com/rails/rails/issues/37270#issuecomment-553927324
-  around do |example|
-    descendants = ActiveJob::Base.descendants + [ActiveJob::Base]
-    descendants.each(&:disable_test_adapter)
-    ActiveJob::Base.queue_adapter = :sidekiq
-
-    example.run
-
-    descendants.each { |a| a.queue_adapter = :test }
-  end
-
-  it 'sets retries for mailers to 3', quarantine: 'https://gitlab.com/gitlab-org/gitlab/-/issues/332645' do
+RSpec.describe 'Mailer retries', :sidekiq_mailers do
+  it 'sets retries for mailers to 3' do
     DeviseMailer.user_admin_approval(create(:user)).deliver_later
 
     expect(Sidekiq::Queues['mailers'].first).to include('retry' => 3)

spec/lib/marginalia_spec.rb

@@ -89,21 +89,7 @@ RSpec.describe 'Marginalia spec' do
       end
     end
 
-    describe 'for ActionMailer delivery jobs' do
-      # We need to ensure that this runs through Sidekiq to take
-      # advantage of the middleware. There is a Rails bug that means we
-      # have to do some extra steps to make this happen:
-      # https://github.com/rails/rails/issues/37270#issuecomment-553927324
-      around do |example|
-        descendants = ActiveJob::Base.descendants + [ActiveJob::Base]
-        descendants.each(&:disable_test_adapter)
-        ActiveJob::Base.queue_adapter = :sidekiq
-
-        example.run
-
-        descendants.each { |a| a.queue_adapter = :test }
-      end
-
+    describe 'for ActionMailer delivery jobs', :sidekiq_mailers do
       let(:delivery_job) { MarginaliaTestMailer.first_user.deliver_later }
 
       let(:recorded) do

spec/services/notification_service_spec.rb

@@ -929,6 +929,10 @@ RSpec.describe NotificationService, :mailer do
       end
 
       context 'design management is disabled' do
+        before do
+          enable_design_management(false)
+        end
+
         it 'does not notify anyone' do
           notification.new_note(note)
 

spec/support/sidekiq.rb

@@ -20,4 +20,25 @@ RSpec.configure do |config|
   config.around(:example, :sidekiq_inline) do |example|
     gitlab_sidekiq_inline { example.run }
   end
+
+  # Some specs need to run mailers through Sidekiq explicitly, rather
+  # than the ActiveJob test adapter. There is a Rails bug that means we
+  # have to do some extra steps to make this happen:
+  # https://github.com/rails/rails/issues/37270
+  #
+  # In particular, we can't use an `around` hook because then the 'before' part
+  # of that will run before the `before_setup` hook in ActiveJob::TestHelper,
+  # which doesn't do what we want.
+  #
+  config.before(:example, :sidekiq_mailers) do
+    queue_adapter_changed_jobs.each { |k| k.queue_adapter = :sidekiq }
+    queue_adapter_changed_jobs.each(&:disable_test_adapter)
+  end
+
+  config.after(:example, :sidekiq_mailers) do
+    queue_adapter_changed_jobs.each do |klass|
+      klass.queue_adapter = :test
+      klass.enable_test_adapter(ActiveJob::QueueAdapters::TestAdapter.new)
+    end
+  end
 end