From: Paul Brannan <pbrannan@...>
Date: 2003-01-23T06:32:31+09:00
Subject: Re: iterating in a test

On Wed, Jan 22, 2003 at 03:31:01PM +0900, nathaniel@NOSPAMtalbott.ws wrote:
>   def performing_action(message) # Not tested
>     @message_stack ||= []
>     @message_stack.push(message)
>     begin
>       yield
>     rescue Exception
>       raise $!, [$!.message, *@message_stack].join("\n"), $!.backtrace
>     ensure
>       @message_stack.pop
>     end
>   end

This works well in Ruby 1.7/1.8.  In Ruby 1.6 this doesn't work as well,
though:

  class Exc < Exception
    def initialize(a, b, c)
      super("Exception: #{a}, #{b}, #{c}")
    end
  end

  performing_action('playing with Ruby') do
    performing_action('doing some silly things') do
      raise Exc.new(1, 2, 3)
    end
  end

  [pbrannan@zaphod tmp]$ ruby -v
  ruby 1.6.8 (2002-12-24) [i686-linux]
  [pbrannan@zaphod tmp]$ ruby test.rb
  test.rb:7:in `initialize': wrong # of arguments(1 for 3) (ArgumentError)
  playing with Ruby
          from test.rb:7:in `exception'
          from test.rb:7:in `raise'
          from test.rb:7:in `performing_action'
          from test.rb:32
          from test.rb:31:in `performing_action'
          from test.rb:31

So instead I have:

  def performing_action(action)
    begin
      yield
    ensure
      $!.message.replace($!.message + "\n\twhile " + action) if $!
    end
  end

  [pbrannan@zaphod tmp]$ ruby test.rb
  test.rb:32: Exception: 1, 2, 3 (Exc)
          while doing some silly things
          while playing with Ruby
          from test.rb:31:in `performing_action'
          from test.rb:31
          from test.rb:30:in `performing_action'
          from test.rb:30

Or alternately:

  module ExceptionActions
    attr_reader :actions

    def self.extend_object(obj)
      super(obj)
      obj.instance_eval { @actions = [] }
    end

    def to_s
      return super + @actions.map { |a| "\n\twhile #{a}" }.join
    end

    alias_method :message, :to_s
    alias_method :to_str, :to_s
  end

  def performing_action(action)
    begin
      yield
    ensure
      if $! then
        if not ExceptionActions === exc then
          $!.extend(ExceptionActions)
        end
        $!.actions.push(action)
      end
    end
  end

The latter solution is a little more verbose but also a little more
robust (it still works even if $!.message is not a string).

> It's seems overly complex for me to want to use it, though; if the
> simpler solution I gave above wouldn't work, I'd probably start looking
> to refactor my tests. Just my $0.02.

Refactoring my tests is what brought this about.  I had many tests doing
very similar things, but varying by only a few parameters.  My solution
was to consolidate those tests into a few small tests.  Perhaps there's
a better solution that I'm not aware of.

Paul