FEATURE: Allow theme tests to be run in production (#12815)

This commit allows site admins to run theme tests in production via a new `/theme-qunit` route. When you visit `/theme-qunit`, you'll see a list of the themes/components installed on your site that have tests, and from there you can select a theme or component that you run its tests.

We also have a new rake task `themes:install_and_test` that can be used to install a list of themes/components on a temporary database and run the tests of the themes/components that are installed. This rake task can be useful when upgrading/deploying a Discourse instance to make sure that the installed themes/components are compatible with the new Discourse version being deployed, and if the tests fail you can abort the build/deploy process so you don't end up with a broken site.

app/controllers/qunit_controller.rb

@@ -11,16 +11,52 @@ class QunitController < ApplicationController
   # only used in test / dev
   def index
     raise Discourse::InvalidAccess.new if Rails.env.production?
-    if (theme_name = params[:theme_name]).present?
-      theme = Theme.find_by(name: theme_name)
-      raise Discourse::NotFound if theme.blank?
-    elsif (theme_url = params[:theme_url]).present?
-      theme = RemoteTheme.find_by(remote_url: theme_url)
-      raise Discourse::NotFound if theme.blank?
+  end
+
+  def theme
+    raise Discourse::NotFound.new if !can_see_theme_qunit?
+
+    param_key = nil
+    @suggested_themes = nil
+    if (id = get_param(:id)).present?
+      theme = Theme.find_by(id: id.to_i)
+      param_key = :id
+    elsif (name = get_param(:name)).present?
+      theme = Theme.find_by(name: name)
+      param_key = :name
+    elsif (url = get_param(:url)).present?
+      theme = RemoteTheme.find_by(remote_url: url)&.theme
+      param_key = :url
     end
-    if theme.present?
-      request.env[:resolved_theme_ids] = [theme.id]
-      request.env[:skip_theme_ids_transformation] = true
+
+    if param_key && theme.blank?
+      return render plain: "Can't find theme with #{param_key} #{params[param_key].inspect}", status: :not_found
     end
+
+    if !param_key
+      @suggested_themes = Theme
+        .where(
+          id: ThemeField.where(target_id: Theme.targets[:tests_js]).distinct.pluck(:theme_id)
+        )
+        .order(updated_at: :desc)
+        .pluck(:id, :name)
+      return
+    end
+
+    request.env[:resolved_theme_ids] = [theme.id]
+    request.env[:skip_theme_ids_transformation] = true
+  end
+
+  protected
+
+  def can_see_theme_qunit?
+    return true if !Rails.env.production?
+    current_user&.admin?
+  end
+
+  private
+
+  def get_param(key)
+    params[:"theme_#{key}"] || params[key]
   end
 end