parallel_tests ruby Rubygems

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

3 years after

Speedup Test::Unit + RSpec + Cucumber by running parallel on multiple CPUs (or cores).
ParallelTests splits tests into even groups(by number of tests or runtime) and runs each group in a single process with its own database.

upgrading from 0.6 ?

Setup for Rails

still using Rails 2?


If you use RSpec: ensure you got >= 2.4

As gem

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

OR as plugin

rails plugin install git://

# add to Gemfile
gem "parallel", :group => :development

Add to config/database.yml

ParallelTests uses 1 database per test-process, 2 processes will use *_test and *_test2.

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

Create additional database(s)

rake parallel:create

Copy development schema (repeat after migrations)

rake parallel:prepare


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 by pattern (e.g. use one integration server per subfolder / see if you broke any 'user'-related tests)

rake parallel:test[^test/unit] # every test file in test/unit folder
rake parallel:test[user]  # run users_controller + user_helper + user tests
rake parallel:test['user|product']  # run user and product related tests

Example output

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

843 examples, 0 failures, 1 pending

Took 29.925333 seconds


Even process runtimes

Log test runtime to give each process the same runtime.

Rspec: Add to your .rspec_parallel (or .rspec) :

If installed as plugin: -I vendor/plugins/parallel_tests/lib
--format progress
--format ParallelTests::RSpec::RuntimeLogger --out tmp/parallel_runtime_rspec.log

Test::Unit: Add to your test_helper.rb:

require 'parallel_tests/test/runtime_logger'

RSpec: SummaryLogger

This logger logs the test output without the different processes overwriting each other.

Add the following to your .rspec_parallel (or .rspec) :

If installed as plugin: -I vendor/plugins/parallel_tests/lib
--format progress
--format ParallelTests::RSpec::SummaryLogger --out tmp/spec_summary.log

RSpec: FailuresLogger

This logger produces pasteable command-line snippets for each failed example.


rspec /path/to/my_spec.rb:123 # should do something

Add the following to your .rspec_parallel (or .rspec) :

If installed as plugin: -I vendor/plugins/parallel_tests/lib
--format progress
--format ParallelTests::RSpec::FailuresLogger --out tmp/failing_specs.log

Setup for non-rails

gem install parallel_tests
# go to your project dir
parallel_test test/
parallel_rspec spec/
parallel_cucumber features/
  • use ENV['TEST_ENV_NUMBER'] inside your tests to select separate db/memcache/etc.
  • Only run selected files & folders:

    parallel_test test/bar test/baz/foo_text.rb

Options are: -n [PROCESSES] How many processes to use, default: available CPUs -p, --pattern [PATTERN] run tests matching this pattern --group-by group tests by: found - order of finding files steps - number of cucumber steps default - runtime or filesize -m, --multiply-processes [FLOAT] use given number as a multiplier of processes to run -s, --single [PATTERN] Run all matching files in only one process -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] test(default) / rspec / cucumber --non-parallel execute same commands but do not in parallel, needs --exec --chunk-timeout [TIMEOUT] timeout before re-printing the output of a child-process -v, --version Show Version -h, --help Show this.

You can run any kind of code in parallel 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 .rspec_parallel to use different options, e.g. no --drb
  • [RSpec] delete script/spec
  • [Spork] does not work with parallel_tests
  • [RSpec] remove --loadby from you spec/*.opts
  • [RSpec] Instantly see failures (instead of just a red F) with rspec-instafail
  • [Bundler] if you have a Gemfile then bundle exec will be used to run tests
  • [Cucumber] add a parallel: foo profile to your config/cucumber.yml and it will be used to run parallel tests
  • Capybara setup
  • Sphinx setup
  • Capistrano setup let your tests run on a big box instead of your laptop
  • [SQL schema format] use :ruby schema format to get faster parallel:prepare`
  • [ActiveRecord] if you do not have db:abort_if_pending_migrations add this to your Rakefile: task('db:abort_if_pending_migrations'){}
  • export PARALLEL_TEST_PROCESSORS=X in your environment and parallel_tests will use this number of processors by default
  • [ZSH] use quotes to use rake arguments rake "parallel:prepare[3]"
  • email_spec and/or action_mailer_cache_delivery


  • add unit tests for cucumber runtime formatter
  • make jRuby compatible basics
  • make windows compatible


inspired by pivotal labs


Michael Grosser
[email protected]
License: MIT

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