# File activesupport/lib/active_support/test_case.rb, line 79
def parallelize(workers: :number_of_processors, with: :processes, threshold: ActiveSupport.test_parallelization_threshold)
  workers = Concurrent.physical_processor_count if workers == :number_of_processors
  workers = ENV["PARALLEL_WORKERS"].to_i if ENV["PARALLEL_WORKERS"]

  return if workers <= 1

  Minitest.parallel_executor = ActiveSupport::Testing::ParallelizeExecutor.new(size: workers, with: with, threshold: threshold)
end

Parallelizes the test suite.

Takes a workers argument that controls how many times the process is forked. For each process a new database will be created suffixed with the worker number.

test-database-0
test-database-1

If ENV["PARALLEL_WORKERS"] is set the workers argument will be ignored and the environment variable will be used instead. This is useful for CI environments, or other environments where you may need more workers than you do for local testing.

If the number of workers is set to 1 or fewer, the tests will not be parallelized.

If workers is set to :number_of_processors, the number of workers will be set to the actual core count on the machine you are on.

The default parallelization method is to fork processes. If you'd like to use threads instead you can pass with: :threads to the parallelize method. Note the threaded parallelization does not create multiple database and will not work with system tests at this time.

parallelize(workers: :number_of_processors, with: :threads)

The threaded parallelization uses minitest's parallel executor directly. The processes parallelization uses a Ruby DRb server.

Because parallelization presents an overhead, it is only enabled when the number of tests to run is above the threshold param. The default value is 50, and it's configurable via config.active_support.test_parallelization_threshold.

# File activesupport/lib/active_support/test_case.rb, line 101
def parallelize_setup(&block)
  ActiveSupport::Testing::Parallelization.after_fork_hook(&block)
end

Set up hook for parallel testing. This can be used if you have multiple databases or any behavior that needs to be run after the process is forked but before the tests run.

Note: this feature is not available with the threaded parallelization.

In your test_helper.rb add the following:

class ActiveSupport::TestCase
  parallelize_setup do
    # create databases
  end
end

# File activesupport/lib/active_support/test_case.rb, line 118
def parallelize_teardown(&block)
  ActiveSupport::Testing::Parallelization.run_cleanup_hook(&block)
end

Clean up hook for parallel testing. This can be used to drop databases if your app uses multiple write/read databases or other clean up before the tests finish. This runs before the forked process is closed.

Note: this feature is not available with the threaded parallelization.

In your test_helper.rb add the following:

class ActiveSupport::TestCase
  parallelize_teardown do
    # drop databases
  end
end

# File activesupport/lib/active_support/test_case.rb, line 42
def test_order
  ActiveSupport.test_order ||= :random
end

Returns the order in which test cases are run.

ActiveSupport::TestCase.test_order # => :random

Possible values are :random, :parallel, :alpha, :sorted. Defaults to :random.

# File activesupport/lib/active_support/test_case.rb, line 32
def test_order=(new_order)
  ActiveSupport.test_order = new_order
end

Sets the order in which test cases are run.

ActiveSupport::TestCase.test_order = :random # => :random

Valid values are:

• :random (to run tests in random order)

• :parallel (to run tests in parallel)

• :sorted (to run tests alphabetically by method name)

• :alpha (equivalent to :sorted)