tests: add missing controller tests.

test/functional/robots_controller_test.rb

@@ -0,0 +1,10 @@
+require "test_helper"
+
+class RobotsControllerTest < ActionDispatch::IntegrationTest
+  context "index action" do
+    should "work" do
+      get robots_path(format: :text)
+      assert_response :success
+    end
+  end
+end