run_in_isolation

# File activesupport/lib/active_support/testing/isolation.rb, line 69
        def run_in_isolation(&blk)
          require "tempfile"

          if ENV["ISOLATION_TEST"]
            yield
            test_result = defined?(Minitest::Result) ? Minitest::Result.from(self) : dup
            File.open(ENV["ISOLATION_OUTPUT"], "w") do |file|
              file.puts [Marshal.dump(test_result)].pack("m")
            end
            exit!
          else
            Tempfile.open("isolation") do |tmpfile|
              env = {
                "ISOLATION_TEST" => self.class.name,
                "ISOLATION_OUTPUT" => tmpfile.path
              }

              test_opts = "-n#{self.class.name}##{name}"

              load_path_args = []
              $-I.each do |p|
                load_path_args << "-I"
                load_path_args << File.expand_path(p)
              end

              child = IO.popen([env, Gem.ruby, *load_path_args, $0, *ORIG_ARGV, test_opts])

              begin
                Process.wait(child.pid)
              rescue Errno::ECHILD # The child process may exit before we wait
                nil
              end

              return tmpfile.read.unpack1("m")
            end
          end
        end