Faster Rails Tests

An example app

This example app demonstrates some techniques to dramatically increase the speed of your Rails test, whilst writing highly cohesive code. This example only covers unit tests designed to be run as part of a red/green/refactor cycle, and expects that there would be a separate integration suite which would be run before committing code.

Please checkout the slides from my Magrails conference presentation or my blog post for more specific details.

master branch

Start in the master branch - initially our logic to calculate the discount is in the Basket model. Try running the following and note the time it takes to run the tests:

bundle
rake db:test:prepare
time bundle exec rake spec
time bundle exec rspec spec
time rspec spec

extract_business_logic_into_modules

Checkout extract_business_logic_into_modules, this is the first refactor - the business logic has been moved into lib/discount_caclulator.rb, which is included into the Basket - see the difference in test times:

time bundle exec rake spec
time bundle exec rspec spec
time rspec spec

note that as sum is an Active Support core extension, and we're not including Rails, the method has been changed to use inject(:+) 1.9.2 specific

extract_domain_objects_into_classes branch

Checkout extract_domain_objects_into_classes, the logic has been extracted into a class:

time bundle exec rake spec
time bundle exec rspec spec
time rspec spec

including_specific_parts_of_rails branch

This example demonstrates inclusion of specific parts of rails, in this case we revert to sum and include Active Suppoort's Enumerable core extensions in the test:

time rspec spec_no_rails

testing_helpers_without_rails branch

This example demonstrates a way to test Rails helpers without including Rails

loads_of_tests branch

This example contains 1000 specs - and whilst this is a convtrived example, it's included here to demonstrate how this approach could work on a larger scale - for me these specs run in under a second

Further reading

This example taken from real life code, refactoring inspired by Corey Haines' talk at Golden Gate Ruby Conf

• coreyhaines - confreaks.net/videos/641-gogaruco2011-fast-rails-tests
• garybernhardt - destroyallsoftware.com
• martinfowler - objectmentor.com/resources/articles/srp.pdf