Merge pull request #41684 from ricardotk002/disable-parallel-testing

Disable parallel testing when running individual files

activesupport/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Tests parallelization is now disabled when running individual files to prevent the setup overhead.
+
+    It can still be enforced if the environment variable `PARALLEL_WORKERS` is present and set to a value greater than 1.
+
+    *Ricardo Díaz*
+
 *   Fix proxying keyword arguments in `ActiveSupport::CurrentAttributes`.
 
     *Marcin Kołodziej*

activesupport/lib/active_support.rb

@@ -87,6 +87,11 @@ module ActiveSupport
   end
 
   cattr_accessor :test_order # :nodoc:
+  cattr_accessor :test_parallelization_disabled, default: false # :nodoc:
+
+  def self.disable_test_parallelization!
+    self.test_parallelization_disabled = true unless ENV["PARALLEL_WORKERS"]
+  end
 
   def self.to_time_preserves_timezone
     DateAndTime::Compatibility.preserve_timezone

activesupport/lib/active_support/test_case.rb

@@ -75,7 +75,7 @@ module ActiveSupport
         workers = Concurrent.physical_processor_count if workers == :number_of_processors
         workers = ENV["PARALLEL_WORKERS"].to_i if ENV["PARALLEL_WORKERS"]
 
-        return if workers <= 1
+        return if workers <= 1 || ActiveSupport.test_parallelization_disabled
 
         executor = case with
                    when :processes
@@ -91,6 +91,12 @@ module ActiveSupport
         Minitest.parallel_executor = executor
 
         parallelize_me!
+
+        # `Minitest::Test.parallelize_me!` will try to change `test_order` to return
+        # `:parallel`. However, since `ActiveSupport::TestCase` is already overriding it,
+        # in some inheritance situations, it will have precedence over the `Minitest` one.
+        # For this reason, it needs to be updated by hand.
+        self.test_order = :parallel
       end
 
       # Set up hook for parallel testing. This can be used if you have multiple

railties/lib/rails/test_unit/runner.rb

@@ -3,6 +3,7 @@
 require "shellwords"
 require "method_source"
 require "rake/file_list"
+require "active_support"
 require "active_support/core_ext/module/attribute_accessors"
 
 module Rails
@@ -46,7 +47,8 @@ module Rails
 
           tests = Rake::FileList[patterns.any? ? patterns : default_test_glob]
           tests.exclude(default_test_exclude_glob) if patterns.empty?
-
+          # Disable parallel testing if there's only one test file to run.
+          ActiveSupport.disable_test_parallelization! if tests.size <= 1
           tests.to_a.each { |path| require File.expand_path(path) }
         end
 

railties/test/application/test_runner_test.rb

@@ -539,6 +539,76 @@ module ApplicationTests
       assert_no_match "create_table(:users)", output
     end
 
+    def test_parallel_is_disabled_when_single_file_is_run
+      exercise_parallelization_regardless_of_machine_core_count(with: :processes, force: false)
+
+      file_name = app_file "test/unit/parallel_test.rb", <<-RUBY
+        require "test_helper"
+
+        class ParallelTest < ActiveSupport::TestCase
+          def test_verify_test_order
+            puts "Test order: \#{self.class.test_order}"
+          end
+        end
+      RUBY
+
+      output = run_test_command(file_name)
+
+      assert_match "Test order: random", output
+    end
+
+    def test_parallel_is_enabled_when_multiple_files_are_run
+      exercise_parallelization_regardless_of_machine_core_count(with: :processes, force: false)
+
+      file_1 = app_file "test/unit/parallel_test_first.rb", <<-RUBY
+        require "test_helper"
+
+        class ParallelTestFirst < ActiveSupport::TestCase
+          def test_verify_test_order
+            puts "Test order (file 1): \#{self.class.test_order}"
+          end
+        end
+      RUBY
+
+      file_2 = app_file "test/unit/parallel_test_second.rb", <<-RUBY
+        require "test_helper"
+
+        class ParallelTestSecond < ActiveSupport::TestCase
+          def test_verify_test_order
+            puts "Test order (file 2): \#{self.class.test_order}"
+          end
+        end
+      RUBY
+
+      output = run_test_command([file_1, file_2].join(" "))
+
+      assert_match "Test order (file 1): parallel", output
+      assert_match "Test order (file 2): parallel", output
+    end
+
+    def test_parallel_is_enabled_when_PARALLEL_WORKERS_is_set
+      @old = ENV["PARALLEL_WORKERS"]
+      ENV["PARALLEL_WORKERS"] = "5"
+
+      exercise_parallelization_regardless_of_machine_core_count(with: :processes, force: false)
+
+      file_name = app_file "test/unit/parallel_test.rb", <<-RUBY
+        require "test_helper"
+
+        class ParallelTest < ActiveSupport::TestCase
+          def test_verify_test_order
+            puts "Test order: \#{self.class.test_order}"
+          end
+        end
+      RUBY
+
+      output = run_test_command(file_name)
+
+      assert_match "Test order: parallel", output
+    ensure
+      ENV["PARALLEL_WORKERS"] = @old
+    end
+
     def test_run_in_parallel_with_process_worker_crash
       exercise_parallelization_regardless_of_machine_core_count(with: :processes)
 
@@ -1039,11 +1109,28 @@ module ApplicationTests
         RUBY
       end
 
-      def exercise_parallelization_regardless_of_machine_core_count(with:)
+      def exercise_parallelization_regardless_of_machine_core_count(with:, force: true)
+        file_content = ERB.new(<<-ERB, trim_mode: "-").result_with_hash(with: with.to_s, force: force)
+          ENV["RAILS_ENV"] ||= "test"
+          require_relative "../config/environment"
+          require "rails/test_help"
+
+          class ActiveSupport::TestCase
+            <%- if force -%>
+            # Force parallelization, even with single files
+            ActiveSupport.test_parallelization_disabled = false
+            <%- end -%>
+
+            # Run tests in parallel with specified workers
+            parallelize(workers: 2, with: :<%= with %>)
+
+            # Setup all fixtures in test/fixtures/*.yml for all tests in alphabetical order.
+            fixtures :all
+          end
+        ERB
+
         app_path("test/test_helper.rb") do |file_name|
-          file = File.read(file_name)
+          File.write(file_name, file_content)
-          file.sub!(/parallelize\(([^)]*)\)/, "parallelize(workers: 2, with: :#{with})")
-          File.write(file_name, file)
         end
       end