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Rails: 2 CPUs = 2x Testing Speed for RSpec, Test::Unit and Cucumber

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Speedup Test::Unit + RSpec + Cucumber by running parallel on multiple CPUs.

Setup for Rails


Rails 3

As gem sudo gem install parallel_tests # add to Gemfile gem "parallel_tests", :group=>:development

OR as plugin sudo gem install parallel rails plugin install git://

Rails 2

As gem sudo gem install parallel_tests # add to config/environments/development.rb config.gem "parallel_tests" # add to Rakefile begin; require 'parallel_tests/tasks'; rescue LoadError; end

OR as plugin

sudo gem install parallel
./script/plugin install git://


1: Add to config/database.yml

  database: xxx_test<%= ENV['TEST_ENV_NUMBER'] %>

2: Create additional database(s)

rake parallel:create

3: Copy development schema (repeat after migrations)

rake parallel:prepare

4: Run!

rake parallel:test          # Test::Unit
rake parallel:spec          # RSpec
rake parallel:features      # Cucumber

rake parallel:test[1] --> force 1 CPU --> 86 seconds
rake parallel:test    --> got 2 CPUs? --> 47 seconds
rake parallel:test    --> got 4 CPUs? --> 26 seconds

Test just a subfolder (e.g. use one integration server per subfolder) rake parallel:test[models] rake parallel:test[something/else]

partial paths are OK too...
rake parallel:test[functional] == rake parallel:test[fun]

Example output

2 processes for 210 specs, ~ 105 specs per process
... test output ...

877 examples, 0 failures, 11 pending
843 examples, 0 failures, 1 pending

Took 29.925333 seconds

Even process runtimes (for specs only atm)

Add to your spec/parallel_spec.opts (or spec/spec.opts) : --format ParallelSpecs::SpecRuntimeLogger:tmp/parallel_profile.log It will log test runtime and partition the test-load accordingly.

Setup for non-rails

sudo gem install parallel_tests
# go to your project dir
parallel_test OR parallel_spec OR parallel_cucumber
# [Optional] use ENV['TEST_ENV_NUMBER'] inside your tests to select separate db/memcache/etc.

[optional] Only run selected files & folders: parallel_test test/bar test/baz/xxx_text.rb

Options are: -n [PROCESSES] How many processes to use, default: available CPUs -p, --path [PATH] run tests inside this path only --no-sort do not sort files before running them -m, --multiply-processes [FLOAT] use given number as a multiplier of processes to run -r, --root [PATH] execute test commands from this path -e, --exec [COMMAND] execute this code parallel and with ENV['TEST_ENV_NUM'] -o, --test-options '[OPTIONS]' execute test commands with those options -t, --type [TYPE] which type of tests to run? test, spec or features -v, --version Show Version -h, --help Show this.

You can run any kind of code with -e / --execute parallel_test -n 5 -e 'ruby -e "puts %[hello from process #{ENV[:TEST_ENV_NUMBER.to_s].inspect}]"' hello from process "2" hello from process "" hello from process "3" hello from process "5" hello from process "4"

1 Process2 Processes4 Processes
RSpec spec-suite18s14s10s


  • [RSpec] add a spec/parallel_spec.opts to use different options, e.g. no --drb (default: spec/spec.opts)
  • [RSpec] if something looks fishy try to delete script/spec
  • [RSpec] if script/spec is missing parallel:spec uses just spec (which solves some issues with double-loaded environment.rb)
  • [RSpec] 'script/spec_server' or spork do not work in parallel
  • [RSpec] ./script/generate rspec if you are running rspec from gems (this plugin uses script/spec which may fail if rspec files are outdated)
  • [Bundler] if you have a Gemfile then bundle exec will be used to run tests
  • with zsh this would be rake "parallel:prepare[3]"


  • make jRuby compatible basics
  • make windows compatible


inspired by pivotal labs


Michael Grosser
Hereby placed under public domain, do what you want, just do not hold me accountable...

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