DEV: Add the 'n_plus_one_control' gem to tests

This gem provides new RSpec matchers helping us to make sure we’re not
creating N+1 queries. It works differently than some other alternatives
as here we don’t have to provide how many queries we expect. The tool
will vary the number of records in the DB and will raise an error
if the number of queries has changed.

A small example has been added in this patch.

Docs at: https://github.com/palkan/n_plus_one_control

Gemfile

@@ -147,6 +147,7 @@ group :test do
   gem "selenium-webdriver", require: false
   gem "test-prof"
   gem "webdrivers", require: false
+  gem "n_plus_one_control"
 end
 
 group :test, :development do

Gemfile.lock

@@ -234,6 +234,7 @@ GEM
     multi_json (1.15.0)
     multi_xml (0.6.0)
     mustache (1.1.1)
+    n_plus_one_control (0.6.2)
     net-http (0.3.2)
       uri
     net-imap (0.3.4)
@@ -583,6 +584,7 @@ DEPENDENCIES
   mocha
   multi_json
   mustache
+  n_plus_one_control
   net-http
   net-imap
   net-pop

lib/topic_view.rb

@@ -820,7 +820,7 @@ class TopicView
   def find_topic(topic_or_topic_id)
     return topic_or_topic_id if topic_or_topic_id.is_a?(Topic)
     # with_deleted covered in #check_and_raise_exceptions
-    Topic.with_deleted.includes(:category, :tags).find_by(id: topic_or_topic_id)
+    Topic.with_deleted.includes(:category).find_by(id: topic_or_topic_id)
   end
 
   def unfiltered_posts

spec/lib/topic_view_spec.rb

@@ -1076,13 +1076,22 @@ RSpec.describe TopicView do
   describe "#tags" do
     subject(:topic_view_tags) { topic_view.tags }
 
-    let(:topic_view) { described_class.new(topic, user) }
+    let(:topic_view) { described_class.new(topic) }
     let(:topic) { Fabricate.build(:topic, tags: tags) }
     let(:tags) { Fabricate.build_times(2, :tag) }
-    let(:user) { Fabricate(:user) }
 
     it "returns the tags names" do
       expect(topic_view_tags).to match tags.map(&:name)
     end
+
+    context "with N+1", :n_plus_one do
+      let!(:topic) { Fabricate(:topic) }
+
+      populate { |n| topic.tags = Fabricate.times(n, :tag) }
+
+      specify do
+        expect { described_class.new(topic.id).tags }.to perform_constant_number_of_queries
+      end
+    end
   end
 end

spec/rails_helper.rb

@@ -62,6 +62,7 @@ require "test_prof/before_all/adapters/active_record"
 require "webdrivers"
 require "selenium-webdriver"
 require "capybara/rails"
+require "n_plus_one_control/rspec"
 
 # The shoulda-matchers gem no longer detects the test framework
 # you're using or mixes itself into that framework automatically.