# Test/unit question. Accessing class variables?

**URL:** <https://www.ruby-forum.com/t/test-unit-question-accessing-class-variables/120230>\
**Category:** Ruby\
**Created:** [November 14, 2007, 11:15pm UTC](https://www.ruby-forum.com/t/test-unit-question-accessing-class-variables/120230 "2007-11-14T23:15:27Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [November 14, 2007, 11:15pm UTC](https://www.ruby-forum.com/t/test-unit-question-accessing-class-variables/120230/1 "2007-11-14T23:15:27Z")

</div>

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.

TIA. G

---

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**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [November 15, 2007, 2:49am UTC](https://www.ruby-forum.com/t/test-unit-question-accessing-class-variables/120230/2 "2007-11-15T02:49:55Z")

</div>

On Nov 14, 2007, at 5:15 PM, removed\_email\_address@domain.invalid wrote:

> NameError: uninitialized class variable @@bad\_users in FindUsersTest  
> end  
> v.parse(“yes”)
> 
> def return\_whatisit  
> 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

---

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**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [November 15, 2007, 4:26am UTC](https://www.ruby-forum.com/t/test-unit-question-accessing-class-variables/120230/3 "2007-11-15T04:26:54Z")

</div>

On 15 Nov 2007, at 07:15, removed\_email\_address@domain.invalid wrote:

> NameError: uninitialized class variable @@bad\_users in FindUsersTest  
> end  
> v.parse(“yes”)
> 
> 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?

The class ‘SimpleTest’ has nothing to do with your class ‘Simple’.  
They share a name but nothing else so you can’t access the class  
variable directly.

> TIA. G

The approach you suggest (defining an extra helper method in the test)  
seems to work fine though?

[alexg@powerbook]/Users/alexg/Desktop(6): cat simple.rb  
class Simple  
@@whatisit = “false”

def parse(n)  
@@whatisit = true if n =~ /yes/  
end  
end  
[alexg@powerbook]/Users/alexg/Desktop(7): cat test.rb  
require ‘simple’  
require ‘test/unit’

class Simple  
def return\_whatisit  
@@whatisit  
end  
end

class SimpleTest \< Test::Unit::TestCase

def test\_parse  
v = Simple.new  
v.parse(“yes”)

```
assert v.return_whatisit

```

end

end  
[alexg@powerbook]/Users/alexg/Desktop(8): ruby test.rb  
Loaded suite test  
Started  
.  
Finished in 0.004223 seconds.

1 tests, 1 assertions, 0 failures, 0 errors

Alex G.

Bioinformatics Center  
Kyoto University

---

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**Author:** ![casper\_the\_ghost](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/c/58956e/32.png) [@casper\_the\_ghost](https://www.ruby-forum.com/u/casper_the_ghost)\
**Post date:** [November 15, 2007, 5:35am UTC](https://www.ruby-forum.com/t/test-unit-question-accessing-class-variables/120230/4 "2007-11-15T05:35:55Z")

</div>

weathercoach wrote:

> 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.

Next time, write the tests at the same time as you write the code. This  
is called “Test Driven Development”, and it usually prevents issues like  
yours before they have a chance to exist.

Specifically, your objects’ interfaces will remain very narrow and  
decoupled. Tests usually sense the program state from convenient return  
values, and private variables remain private.