From: Eric Hodel <drbrain@...7.net>
Date: 2006-04-04T05:59:30+09:00
Subject: Re: Mocking whole classes

On Apr 3, 2006, at 6:37 AM, Thiago Arrais wrote:

> Has anyone tried to mock whole classes (instead of mocking only the  
> objects)?

I've found it more pain than its worth because I change the  
implementation then have to go change all my mocks.  No fun.

> Classes are, like everything else in Ruby, just objects. This allows
> us to mock them just like we would mock any other object. I have been
> working on a Rails application (that will be shared with you as soon
> as I get it translated, I promise) in which I needed to do exactly
> that.
>
> The class I wanted to mock is responsible for communicating to my
> back-end database and fetching the appropriate objects (instances of
> itself). The object-finding functionality is implemented as class
> level methods. If I need the N latest headlines from a reporter named
> 'johnson', I just need to call `Headline.latest(N, "johnson").

When I need that kind of behavior I tend to do something like this:

require 'flickr'

class Flickr

   attr_accessor :responses, :uris

   def open(uri)
     @uris << uri
     yield StringIO.new(@responses.shift)
   end

end

I'm using open-uri so I inject a new open into my class that shadows  
Kernel's open.  My tests prime it with a bunch of responses and when  
I call open I just record the URI and return the in-order response.   
For my test I check that the right URIs were accessed and the right  
data came back.

Here's a test:

class FlickrTest < Test::Unit::TestCase

   def setup
     @flickr = Flickr.new 'API_KEY'
     @flickr.responses = []
     @flickr.uris = []
   end

   def test_find_email
     @flickr.responses << <<-EOF
<?xml version="1.0" encoding="utf-8" ?>
<rsp stat="ok">
         <user id="50178138@N00" nsid="50178138@N00">
                 <username>drbrain</username>
         </user>
</rsp>
     EOF

     nsid = @flickr.find_email :find_email => 'drbrain@segment7.net'

     assert_equal 1, @flickr.uris.length
     assert_equal 'http://flickr.com/services/rest/? 
api_key=API_KEY&find_email=drbrain% 
40segment7.net&method=flickr.people.findByEmail',
                  @flickr.uris.first

     assert_equal '50178138@N00', nsid
   end

end

-- 
Eric Hodel - drbrain@segment7.net - http://blog.segment7.net
This implementation is HODEL-HASH-9600 compliant

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