From: Joel VanderWerf <vjoel@...>
Date: 2008-01-03T04:21:13+09:00
Subject: Re: Dynamically add a method to a TestCase

Achim Domma wrote:
> Hi,
> 
> I'm experimenting with the dynamic features of ruby to add methods to
> a TestCase. Here is my test script:
> 
> require 'watir'
> require 'test/unit'
> 
> class MyTest < Test::Unit::TestCase
> end
> 
> for num in ["a","b","c"]
>     MyTest.send(:define_method,"test_" + num) {
>         assert(false,"->"+num)
>     }
> end
> 
> It works fine so far, but all asserts display "->c" as error message.
> I don't understand why! Any hint? How to fix it?

It's the way the 'for' construct scopes the 'num' variable.  All three 
method definition blocks are seeing 'num' in the same scope, so they all 
get the last assigned value, "c".

Try this:

   procs = []
   for num in ["a","b","c"]
   #["a","b","c"].each do |num|
       procs << proc {
           num
       }
   end

   procs.each do |pr|
     puts pr.call
   end

That prints three 'c's.

Now uncomment the 'each' line and comment out the 'for' line, and you'll 
see the scope difference!

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407