Rake task to run minitests in batches

Rakefile

namespace :test do
  desc "Parallel tests. Use TEST_WORKERS and TEST_WORKER_NUM." \
    "TEST_WORKER_NUM in range from 1..TEST_WORKERS"
  task :parallel do
    workers = ENV.fetch("TEST_WORKERS", 1).to_i
    worker = ENV.fetch("TEST_WORKER_NUM", 1).to_i
    buckets = Array.new(workers) { [] }

    # Fill the buckets
    i = 0
    files = Dir["test/*_test.rb"].entries.sort { |f| File.size(f) }
    files.each do |f|
      i = 0 if buckets.size == i
      buckets[i] << f
      i += 1
    end

    if worker < 1 || worker > workers
      raise "TEST_WORKER_NUM is not correct: #{worker}." \
        "Check that it greater or equal 1 and less or equal TEST_WORKERS: #{workers}"
    end

    files = buckets[worker - 1].join(" ")
    args = "-Ilib:test -r 'rake/rake_test_loader.rb' #{files} -v #{ENV.fetch("TESTOPTS", "")}"
    ruby args do |ok, status|
      if !ok && status.respond_to?(:signaled?) && status.signaled?
        raise SignalException, status.termsig
      elsif !ok
        status  = "Command failed with status (#{status.exitstatus})"
        details = ": [ruby #{args}]"
        message = status + details
        raise message
      end
    end
  end
end

USAGE.md

Running tests in batches

• TEST_WORKERS - Total number of workers or batches. It uses to identify a total number of batches, that would be run in parallel. Default: 1
• TEST_WORKER_NUM - Specify which batch to run. The value is between 1 and TEST_WORKERS. Default: 1

$ bundle exec rake test:parallel TEST_WORKERS=5 TEST_WORKER_NUM=1