From: Robert Dober <robert.dober@...>
Date: 2010-05-24T20:13:19+09:00
Subject: Re: How do I write an RSpec test to unit-test this interesting 	metaprogramming code?

On Sun, May 23, 2010 at 4:00 PM, James Wenton <kkaitan@gmail.com> wrote:
> I'm a little stumped by this problem. Here's some simple code that,
> for each argument specified, will add specific get/set methods named
> after that argument. If you write `attr_option :foo, :bar`, then you
> will see `#foo/foo=` and `#bar/bar=` instance methods on `Config`:
>
>    module Configurator
>      class Config
>        def initialize()
>          @options = {}
>        end
>
>        def self.attr_option(*args)
>          args.each do |a|
>            if not self.method_defined?(a)
>              define_method "#{a}" do
>                @options[:"#{a}"] ||= {}
>              end
>
>              define_method "#{a}=" do |v|
>                @options[:"#{a}"] = v
>              end
>            else
>              throw Exception.new("already have attr_option for #{a}")
>            end
>          end
>        end
>      end
>    end
>
> So far, so good. I want to write some RSpec tests to verify this code
> is actually doing what it's supposed to. But there's a problem! If I
> invoke `attr_option :foo` in one of the test methods, that method is
> now forever defined in Config. So a subsequent test will fail when it
> shouldn't, because `foo` is already defined:
>
>      it "should support a specified option" do
>        c = Configurator::Config
>        c.attr_option :foo
>        # ...
>      end
>
>      it "should support multiple options" do
>        c = Configurator::Config
>        c.attr_option :foo, :bar, :baz   # Error! :foo already defined
>                                         # by a previous test.
>        # ...
>      end
Caleb is right, c is not a good name ;), however

  lambda{ c.attr_option..... }.should raise_error( WhatWasIt)

I call it WhatWasIt because you really should define your own Exception,
e.g.
IllegalMonitorState = Class::new RuntimeError

please take care to subclass RuntimeError, subclassing Exception is
waaaay toooo general.

HTH
R.

>
> Is there a way I can give each test an anonymous "clone" of the
> `Config` class which is independent of the others?
>
>



-- 
The best way to predict the future is to invent it.
-- Alan Kay