rails--rails/activesupport/lib/active_support/testing/isolation.rb

require 'rbconfig'
require 'minitest/parallel_each'

module ActiveSupport
  module Testing
    module Isolation
      require 'thread'

      def self.included(klass) #:nodoc:
        klass.extend(Module.new {
          def test_methods
            ParallelEach.new super
          end
        })
      end

      def self.forking_env?
        !ENV["NO_FORK"] && ((RbConfig::CONFIG['host_os'] !~ /mswin|mingw/) && (RUBY_PLATFORM !~ /java/))
      end

      @@class_setup_mutex = Mutex.new

      def _run_class_setup      # class setup method should only happen in parent
        @@class_setup_mutex.synchronize do
          unless defined?(@@ran_class_setup) || ENV['ISOLATION_TEST']
            self.class.setup if self.class.respond_to?(:setup)
            @@ran_class_setup = true
          end
        end
      end

      def run
        serialized = run_in_isolation do
          super
        end

        Marshal.load(serialized)
      end

      module Forking
        def run_in_isolation(&blk)
          read, write = IO.pipe

          pid = fork do
            read.close
            yield
            write.puts [Marshal.dump(self.dup)].pack("m")
            exit!
          end

          write.close
          result = read.read
          Process.wait2(pid)
          return result.unpack("m")[0]
        end
      end

      module Subprocess
        ORIG_ARGV = ARGV.dup unless defined?(ORIG_ARGV)

        # Crazy H4X to get this working in windows / jruby with
        # no forking.
        def run_in_isolation(&blk)
          require "tempfile"

          if ENV["ISOLATION_TEST"]
            yield
            File.open(ENV["ISOLATION_OUTPUT"], "w") do |file|
              file.puts [Marshal.dump(self.dup)].pack("m")
            end
            exit!
          else
            Tempfile.open("isolation") do |tmpfile|
              ENV["ISOLATION_TEST"]   = self.class.name
              ENV["ISOLATION_OUTPUT"] = tmpfile.path

              load_paths = $-I.map {|p| "-I\"#{File.expand_path(p)}\"" }.join(" ")
              `#{Gem.ruby} #{load_paths} #{$0} #{ORIG_ARGV.join(" ")}`

              ENV.delete("ISOLATION_TEST")
              ENV.delete("ISOLATION_OUTPUT")

              return tmpfile.read.unpack("m")[0]
            end
          end
        end
      end

      include forking_env? ? Forking : Subprocess
    end
  end
end