Rails - Jun 2006 - How to mock a model method for unit tests?

I have a model class, say, model.rb, and in the normal course of things 
it creates an instance of another class, say utility.rb (also in the 
models directory).

class Utility

  def initialize(obj)
    # do stuff...
  end

  def do_something_expensive
    # lots of stuff here
  end

end

During testing, I want to mock out do_something_expensive because it''s 
not important for the tests, but only during development.  So I went to 
the tests\mocks folder and added a file called utility.rb with only 
this:

# this is the mock file
class Utility

  def do_something_expensive
    # shortcut, just return true to satisfy client code
    true
  end

end

So this way, in my tests, when my model uses the Utility class, it 
should be insantiating my mock instead.

But when I rake test:units, I get a syntax error saying that it can''t 
construct a Utility object with the original constructor:  "Wrong number 
of argumes (0 for 1)".

It''s as if the mock class is totally taking over, whereas I just want
to
override the do_something_expensive and leave everything else.

What am I doing wrong?

The Utility class is actually larger than I''m showing here, and
I''m
finding I have to basically copy all of the methods into the mock to get 
it to work.

Jeff

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Jeff Cohen wrote:
> But when I rake test:units, I get a syntax error saying that it
can''t
> construct a Utility object with the original constructor:  "Wrong
number
> of argumes (0 for 1)".
> 
> It''s as if the mock class is totally taking over, whereas I just
want to
> override the do_something_expensive and leave everything else.
> 
> What am I doing wrong?
You need to require the original class so that you''re re-opening it, as
opposed to redefining it from scratch.  Then you can knock out the one 
unwanted function, while leaving all the others intack

Eric

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Posted via http://www.ruby-forum.com/.

On Thursday, June 15, 2006, at 5:42 PM, Eric D. Nielsen
wrote:
>Jeff Cohen wrote:
>> But when I rake test:units, I get a syntax error saying that it
can''t
>> construct a Utility object with the original constructor:  "Wrong
number
>> of argumes (0 for 1)".
>>
>> It''s as if the mock class is totally taking over, whereas I
just want to
>> override the do_something_expensive and leave everything else.
>>
>> What am I doing wrong?
>
>You need to require the original class so that you''re re-opening
it, as
>opposed to redefining it from scratch.  Then you can knock out the one
>unwanted function, while leaving all the others intack
>
>Eric
>
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>Posted via http://www.ruby-forum.com/.
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>Rails mailing list
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you should also put the mocks in the ''test/mock/development''
or ''test/
mock/test'' if you want it to only load during development or testing.

_Kevin

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On Thursday, June 15, 2006, at 5:42 PM, Eric D. Nielsen
wrote:
>>You need to require the original class so that you''re
re-opening it, as
>>http://lists.rubyonrails.org/mailman/listinfo/rails
Doh!!  Thanks a lot, Eric.

Kevin Olbrich wrote:
> you should also put the mocks in the
''test/mock/development'' or ''test/
> mock/test'' if you want it to only load during development or
testing.
> 
> _Kevin
Yes, I forgot to say that I did put it in the test/ folder, but thanks 
for pointing that out.

Jeff

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