Adding a Mention model, test stubs

spec/controllers/xrd_controller_spec.rb

@@ -1,5 +1,11 @@
 require 'rails_helper'
 
 RSpec.describe XrdController, type: :controller do
+  describe 'GET #host_meta' do
+    pending
+  end
 
+  describe 'GET #webfinger' do
+    pending
+  end
 end