From: Morton Goldberg <m_goldberg@...>
Date: 2007-11-15T10:49:17+09:00
Subject: Re: test/unit question.   Accessing class variables?

On Nov 14, 2007, at 5:15 PM, weathercoach@gmail.com wrote:

>    Hello.
>    This is my first attempt in trying to use the ruby library test/
> unit.   Additionally my programming and ruby skills are still around
> the beginner stage.
>
>   I have a unix utility which I've written in ruby and now that it
> actually does some work I want to be able to test it.    My first
> attempt at a unit test was to check the value of a class variable but
> this results in the following error
>
> NameError: uninitialized class variable @@bad_users in FindUsersTest
>
>    Here is a class and test which demonstrates what I'm trying to
> do.
>
> -- start class
> class Simple
> @@whatisit = "false"
>
>   def parse(n)
>     @@whatisit = true if n =~ /yes/
>   end
> end
>
> --- start test
> require 'simple'
> require 'test/unit'
>
> class SimpleTest <  Test::Unit::TestCase
>
>   def test_parse
>    v = Simple.new
>    v.parse("yes")
>
>   assert @@whatisit
>    end
> end
>
> --- run test
> ./test_simple.rb
> Started
> E
> Finished in 0.003813 seconds.
>
>   1) Error:
> test_parse(SimpleTest):
> NameError: uninitialized class variable @@whatisit in SimpleTest
>     ./test_simple.rb:14:in `test_parse'
>
> 1 tests, 0 assertions, 0 failures, 1 errors
>
>
>  I then added this method into the simple class above
>
> def return_whatisit
>   @@whatisit
> end
>
>    Then in my test created a Simple object (v = Simple.new) and then
> called the return_whatisit method (eg: v.return_whatisit).     I dont
> really want to have to add extra methods to the code to support the
> retreival of class variables from within the tests.   I dont
> understand why I'm not able to access the class variable @@whatisit
> from within the test script?    Is it possible to extend the Simple
> class from within the test file itself?
>    For example iin the test file I would like to add this method to
> the Simple class
> def return_whatisit
>   @@whatisit
> end
>
>    So if you have any tips on how to best approach this situation I
> would appreciate it.    I figure if I get a better understanding of
> using and writing tests that will influence how I write scripts down
> the road.

I don't know how to solve your problem under the constraints you  
impose -- that is, with a class variable but without writing some  
kind of accessor method. The following quote from the Pickaxe book  
suggests there is no support for what you want in Ruby.

    Class variables are private to a class and its instances. If you  
want to make them acces-
    sible to the outside world, you’ll need to write an accessor  
method. This method could
    be either an instance method or ... a class method.

Do you really need to use a class variable?

Regards, Morton