FIX: correctly resets user_themes template

This commit adds tests for this behaviour and also adds support for
reseting cache when updating a theme name and destroying a theme.

app/models/theme.rb

@@ -28,7 +28,7 @@ class Theme < ActiveRecord::Base
     changed_fields.each(&:save!)
     changed_fields.clear
 
-    Theme.expire_site_cache! if user_selectable_changed?
+    Theme.expire_site_cache! if user_selectable_changed? || name_changed?
 
     @dependant_themes = nil
     @included_themes = nil
@@ -46,7 +46,6 @@ class Theme < ActiveRecord::Base
     end
 
     if self.id
-
       ColorScheme
         .where(theme_id: self.id)
         .where("id NOT IN (SELECT color_scheme_id FROM themes where color_scheme_id IS NOT NULL)")
@@ -56,6 +55,8 @@ class Theme < ActiveRecord::Base
         .where(theme_id: self.id)
         .update_all(theme_id: nil)
     end
+
+    Theme.expire_site_cache!
   end
 
   after_commit ->(theme) do

spec/models/theme_spec.rb

@@ -10,6 +10,10 @@ describe Theme do
     Fabricate(:user)
   end
 
+  let(:guardian) do
+    Guardian.new(user)
+  end
+
   let :customization_params do
     { name: 'my name', user_id: user.id, header: "my awesome header" }
   end
@@ -214,4 +218,32 @@ HTML
     expect(Theme.user_theme_keys).to eq(Set.new([]))
   end
 
+  it 'correctly caches user_themes template' do
+    Theme.destroy_all
+
+    json = Site.json_for(guardian)
+    user_themes = JSON.parse(json)["user_themes"]
+    expect(user_themes).to eq([])
+
+    theme = Theme.create!(name: "bob", user_id: -1, user_selectable: true)
+    theme.save!
+
+    json = Site.json_for(guardian)
+    user_themes = JSON.parse(json)["user_themes"].map { |t| t["name"] }
+    expect(user_themes).to eq(["bob"])
+
+    theme.name = "sam"
+    theme.save!
+
+    json = Site.json_for(guardian)
+    user_themes = JSON.parse(json)["user_themes"].map { |t| t["name"] }
+    expect(user_themes).to eq(["sam"])
+
+    Theme.destroy_all
+
+    json = Site.json_for(guardian)
+    user_themes = JSON.parse(json)["user_themes"]
+    expect(user_themes).to eq([])
+  end
+
 end