instance method run_in_isolation

# File activesupport/lib/active_support/testing/isolation.rb, line 62
        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,
                ISOLATION_OUTPUT: tmpfile.path
              }

              load_paths = $-I.map {|p| "-I\"#{File.expand_path(p)}\"" }.join(" ")
              orig_args = ORIG_ARGV.join(" ")
              test_opts = "-n#{self.class.name}##{self.name}"
              command = "#{Gem.ruby} #{load_paths} #{$0} #{orig_args} #{test_opts}"

              # IO.popen lets us pass env in a cross-platform way
              child = IO.popen([env, command])

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

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