PERF: Add scheduled job to delete old stylesheet cache rows (#13747)

spec/models/stylesheet_cache_spec.rb

@@ -4,7 +4,7 @@ require 'rails_helper'
 
 describe StylesheetCache do
 
-  describe "add" do
+  describe ".add" do
     it "correctly cycles once MAX_TO_KEEP is hit" do
       StylesheetCache.destroy_all
 
@@ -37,6 +37,26 @@ describe StylesheetCache do
 
       expect(StylesheetCache.order(:id).pluck(:target)).to eq(["desktop", "desktop", "mobile", "mobile"])
     end
+  end
 
+  describe ".clean_up" do
+    it "removes items older than threshold" do
+      StylesheetCache.destroy_all
+
+      StylesheetCache.add("a", "b", "c", "map")
+      StylesheetCache.add("d", "e", "f", "map")
+
+      above_threshold = StylesheetCache::CLEANUP_AFTER_DAYS - 1
+      StylesheetCache.first.update!(created_at: above_threshold.days.ago)
+
+      StylesheetCache.clean_up
+      expect(StylesheetCache.all.size).to eq(2)
+
+      below_threshold = StylesheetCache::CLEANUP_AFTER_DAYS + 1
+      StylesheetCache.first.update!(created_at: below_threshold.days.ago)
+
+      StylesheetCache.clean_up
+      expect(StylesheetCache.all.size).to eq(1)
+    end
   end
 end