run_in_isolation

# File activesupport/lib/active_support/testing/isolation.rb, line 38
        def run_in_isolation(&blk)
          read, write = IO.pipe
          read.binmode
          write.binmode

          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