Add option to set parallel test worker count to the physical core count of the machine (#34735)

* Add option to set parallel test worker count to the physical core count of the machine

Also, use the physical core count of the machine as
the default number of workers, and  generate the `test_helper.rb` file
with `parallelize(workers: :number_of_processors)`

Closes #34734

* Ensure that we always test parallel testing

Since #34734 we decided to use the physical core count of the machine as
the default number of workers in the parallel testing, we need to
ensure that some tests use at least 2 workers because we could
run those tests on VM that has only 1 physical core.
It also fixes tests failures on the CI since Travis server we are using
has only one physical core.
See https://travis-ci.org/rails/rails/jobs/469281088#L2352

1 files changed, 14 insertions, 5 deletions

diff --git a/railties/test/application/test_runner_test.rb b/railties/test/application/test_runner_test.rb
index 140703e118..55cfda82ea 100644
--- a/railties/test/application/test_runner_test.rb
+++ b/railties/test/application/test_runner_test.rb
@@ -523,6 +523,8 @@ module ApplicationTests
     end
 
     def test_run_in_parallel_with_processes
+      substitute_arguments_of_parallelize_method("workers: 2, with: :processes")
+
       file_name = create_parallel_processes_test_file
 
       app_file "db/schema.rb", <<-RUBY
@@ -540,11 +542,7 @@ module ApplicationTests
     end
 
     def test_run_in_parallel_with_threads
-      app_path("/test/test_helper.rb") do |file_name|
-        file = File.read(file_name)
-        file.sub!(/parallelize\(([^\)]*)\)/, "parallelize(\\1, with: :threads)")
-        File.write(file_name, file)
-      end
+      substitute_arguments_of_parallelize_method("workers: 2, with: :threads")
 
       file_name = create_parallel_threads_test_file
 
@@ -563,6 +561,8 @@ module ApplicationTests
     end
 
     def test_run_in_parallel_with_unmarshable_exception
+      substitute_arguments_of_parallelize_method("workers: 2, with: :processes")
+
       file = app_file "test/fail_test.rb", <<-RUBY
         require "test_helper"
         class FailTest < ActiveSupport::TestCase
@@ -587,6 +587,7 @@ module ApplicationTests
     end
 
     def test_run_in_parallel_with_unknown_object
+      substitute_arguments_of_parallelize_method("workers: 2, with: :processes")
       create_scaffold
       app_file "config/environments/test.rb", <<-RUBY
         Rails.application.configure do
@@ -966,6 +967,14 @@ module ApplicationTests
         RUBY
       end
 
+      def substitute_arguments_of_parallelize_method(arguments)
+        app_path("test/test_helper.rb") do |file_name|
+          file = File.read(file_name)
+          file.sub!(/parallelize\(([^\)]*)\)/, "parallelize(#{arguments})")
+          File.write(file_name, file)
+        end
+      end
+
       def create_env_test
         app_file "test/unit/env_test.rb", <<-RUBY
           require 'test_helper'