Media controller specs (#2022)

* Add spec for media controller

* Add MediaAttachment.attached scope

* Simplify methods in media controller

app/controllers/media_controller.rb

@@ -1,16 +1,19 @@
 # frozen_string_literal: true
 
 class MediaController < ApplicationController
-  before_action :set_media_attachment
+  before_action :verify_permitted_status
 
   def show
-    redirect_to @media_attachment.file.url(:original)
+    redirect_to media_attachment.file.url(:original)
   end
 
   private
 
-  def set_media_attachment
-    @media_attachment = MediaAttachment.where.not(status_id: nil).find_by!(shortcode: params[:id])
-    raise ActiveRecord::RecordNotFound unless @media_attachment.status.permitted?(current_account)
+  def media_attachment
+    MediaAttachment.attached.find_by!(shortcode: params[:id])
+  end
+
+  def verify_permitted_status
+    raise ActiveRecord::RecordNotFound unless media_attachment.status.permitted?(current_account)
   end
 end