Rails 5.2 Parallel Tests with RSpec for local and Travis

In order to make our test suite faster, different approaches have been tried:

• parallelize on one VM using parallel_tests gem
• parallelize on mutliple VMs (2) using knapsack gem and matrix with parallel_tests

Regarding the approach using 2 VMs we have system dependencies to install (before_install) with symbolic links which cannot be cached and instantiating 2 VMs to run tests in parallel actually doubles the total time because of that. Also if one job is already taken then the whole test suite will have to wait for that job to complete before starting the next.

While Rails 6 will bring parallel testing, here is how to implement it for Rails 5.2, RSpec and for local and TravisCI.

Install

group :development, :test do
  gem: parallel_tests
end

Database configuration

Append the environment variable TEST_ENV_NUMBER to the test database name in database.yml

default: &default
  adapter: postgresql
  encoding: unicode
  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 8 } %>
test:
  <<: *default
  url: <%= "#{ENV.fetch('DATABASE_URL')}/#{ENV.fetch('DATABASE_NAME')}#{ENV.fetch('TEST_ENV_NUMBER')}" %>

or

test:
  <<: *default
  database: <%= ENV.fetch('DATABASE_NAME') %><%= ENV['TEST_ENV_NUMBER'] %>
  username: ENV['DATABASE_USER']
  password: ENV['DATABASE_PASSWORD']
  host: ENV['DATABASE_HOST']
  port: ENV['DATABASE_PORT']

Create the test databases

One test database is used per thread with the name set previously in the database configuration with the TEST_ENV_NUMBER variable.
parallel_tests will use the number of CPU available by default (including virtual) and this can be overridden.

Run

bundle exec rake parallel:create

override:

bundle exec rake parallel:create[2]

Run RSpec

bundle exec rake parallel:spec

override:

bundle exec rake parallel:spec[2]

Using binstubs

use binstubs to use spring loader for faster tests.
Patch spring to reconnect the database and then force-enabled it by running with DISABLE_SPRING=0

spring configuration

Create config/spring.rb and add

require 'spring/application'
class Spring::Application
  alias connect_database_orig connect_database
  def connect_database
    disconnect_database
    reconfigure_database
    connect_database_orig
end
  def reconfigure_database
    if active_record_configured?
      ActiveRecord::Base.configurations =
        Rails.application.config.database_configuration
    end
  end
end

source: https://github.com/grosser/parallel_tests/wiki/Spring

Run

./bin/rake parallel:spec

Using the command line interface

parallel_rspec spec -n 12

Travis CI

env:
  - RAILS_ENV=test
script:
  - ./bin/rake db:schema:load
  - ./bin/rake parallel:create
  - ./bin/rake parallel:spec

Results

Number of rspec tests: 876

Strategy	Number of processes	Command	Finished in
RSpec	1	bundle exec rspec	2 minutes 2 seconds (122 seconds)
Parallelizing	2 processes	bundle exec rake parallel:spec[2]	1 minute 24 seconds (84 seconds)
Parallelizing	6 processes	bundle exec rake parallel:spec[6]	44 seconds
Parallelizing	12 processes	bundle exec rake parallel:spec[12]	49 seconds
Parallelizing with spring	2 processes	./bin/rake parallel:spec[2]	75 seconds
Parallelizing with spring	6 processes	./bin/rake parallel:spec[6]	42 seconds
Parallelizing with spring	12 processes	./bin/rake parallel:spec	35 seconds