Fix all the errors to get our tests green on Rails 5.1.

spec/requests/robots_txt_controller_spec.rb

@@ -0,0 +1,19 @@
+require 'rails_helper'
+
+RSpec.describe RobotsTxtController do
+  describe '#index' do
+    it "returns index when indexing is allowed" do
+      SiteSetting.allow_index_in_robots_txt = true
+      get '/robots.txt'
+
+      expect(response.body).to include("Disallow: /u/")
+    end
+
+    it "returns noindex when indexing is disallowed" do
+      SiteSetting.allow_index_in_robots_txt = false
+      get '/robots.txt'
+
+      expect(response.body).to_not include("Disallow: /u/")
+    end
+  end
+end