Add retention policy for cached content and media (#19232)

spec/lib/vacuum/system_keys_vacuum_spec.rb

@@ -0,0 +1,22 @@
+require 'rails_helper'
+
+RSpec.describe Vacuum::SystemKeysVacuum do
+  subject { described_class.new }
+
+  describe '#perform' do
+    let!(:expired_system_key) { Fabricate(:system_key, created_at: (SystemKey::ROTATION_PERIOD * 4).ago) }
+    let!(:current_system_key) { Fabricate(:system_key) }
+
+    before do
+      subject.perform
+    end
+
+    it 'deletes the expired key' do
+      expect { expired_system_key.reload }.to raise_error ActiveRecord::RecordNotFound
+    end
+
+    it 'does not delete the current key' do
+      expect { current_system_key.reload }.to_not raise_error
+    end
+  end
+end