run_in_isolation

# File activesupport/lib/active_support/testing/isolation.rb, line 27
        def run_in_isolation(&blk)
          IO.pipe do |read, write|
            read.binmode
            write.binmode

            pid = fork do
              read.close
              yield
              begin
                if error?
                  failures.map! { |e|
                    begin
                      Marshal.dump e
                      e
                    rescue TypeError
                      ex = Exception.new e.message
                      ex.set_backtrace e.backtrace
                      Minitest::UnexpectedError.new ex
                    end
                  }
                end
                test_result = defined?(Minitest::Result) ? Minitest::Result.from(self) : dup
                result = Marshal.dump(test_result)
              end

              write.puts [result].pack("m")
              exit!
            end

            write.close
            result = read.read
            Process.wait2(pid)
            result.unpack1("m")
          end
        end