4 Steps to Faster Rails Tests

This talk was presented at Magrails on October 14th 2011. Check magrails.com for the video, and github.com/seenmyfate for sample code

Transcript

1. 4 Steps to Faster Rails Test Tom Clements Senior Developer, On The Beach tom-clements.com | github.com/seenmyfate @Seenmyfate
2. A question How long does it take to run your unit tests?
3. Let's look at some numbers $ time rake spec 31.486 seconds $ time bundle exec rspec spec 15.741 seconds $ time rspec spec 14.932 seconds
4. And what am I testing?
5. Nothing! # spec/nowt_spec.rb require 'spec_helper' describe "Nothing" do # nada end 0 examples, 0 failures 15.741 seconds total
6. So how can we make this better?
7. Here's some common suggestions Don't Test Get an SSD Use Spork
8. these solutions are just masking the problem And the first part of that problem is spec_helper
9. spec helper is the best way to write really slow painful specs Gary Bernhardt
10. With spec_helper - 15.741 seconds Without:
11. 0.186 seconds # spec/some_spec.rb # require 'spec_helper' describe "Nothing" do # nada end 0 examples, 0 failures 0.186 seconds total
12. So here's the question
13. For our unit tests - Why are we loading the entire rails environment? Because our business logic is in our active record models And we need rails to run tests against classes that inherit from ActiveRecord::Base Because we're breaking SRP
14. Single Responsibility Principle A class should only have one reason to change
15. 4 Steps Extract business logic into modules Extract domain objects into classes Mixin and delegate Test in isolation
16. An example class Basket < ActiveRecord::Base has_many :basket_items def total_discount basket_items.collect(&:discount).sum end end
17. An example require 'spec_helper' describe Basket do context "total_discount" do let(:basket) { Basket.create! } let(:basket_items) { [BasketItem.create!(:discount => 10), BasketItem.create!(:discount => 20) ]} it "should return the total discount" do basket = Basket.create! basket.basket_items = basket_items basket.total_discount.should == 30 end end end
18. 7.092 seconds to run time rspec spec . Finished in 0.24435 seconds 1 example, 0 failures rspec spec 7.092 total
19. Extract behaviour into modules module DiscountCalculator def total_discount basket_items.collect(&:discount). inject(:+) end end
20. Mixin class Basket < ActiveRecord::Base has_many :basket_items include DiscountCalculator end
21. And the test require 'discount_calculator' class FakeBasket include DiscountCalculator end describe DiscountCalculator do context "#total_discount" do it "should return the total discount" do basket = FakeBasket.new basket_items = [stub(:discount => 10), stub(:discount => 20)] basket.stub(:basket_items) { basket_items } basket.total_discount.should eq 30 end end end
22. 0.350 seconds to run time rspec spec . Finished in 0.00121 seconds 1 example, 0 failures rspec spec 0.350 total
23. Extract domain objects into classes class DiscountCalculator def total_discount(items) items.collect(&:discount).inject(:+) end end
24. And delegate class Basket < ActiveRecord::Base has_many :basket_items def total_discount DiscountCalculator.new. total_discount(basket_items) end end
25. And the test require 'discount_calculator' describe DiscountCalculator do context "#total_discount" do let(:items) { [stub(:discount => 10), stub(:discount => 20)] } it "should return the total discount" do calculator = DiscountCalculator.new calculator.total_discount(items).should eq 30 end end end
26. 0.342 seconds to run time rspec spec . Finished in 0.00101 seconds 1 example, 0 failures rspec spec 0.342 total
27. The benefits Higher Cohesion Lightning fast tests Happier developing Try it out github.com/seenmyfate
28. Further viewing/reading @coreyhaines - confreaks.net/videos/641-gogaruco2011-fast-rails- tests @garybernhardt - destroyallsoftware.com @martinfowler - objectmentor.com/resources/articles/srp.pdf
29. 4 Steps to Faster Rails Test Tom Clements Senior Developer, On The Beach tom-clements.com | github.com/seenmyfate @Seenmyfate