Re: [Pyunit-interest] Mock Objects (was Aid requsted regarding test-first-design)

[Dave K. <dk...@bl...>]

At 15:36 24/11/01 -0500, Michal Wallace wrote:
>Hey Dave,
>
>Thanks for writing it. I've read through the code and it's
>pretty slick. :)
>
>I have thought about extending it so that it could recognize
>parameters.
>
>In java, I got used to EasyMock ( http://easymock.org ),
>where you actually have two objects - a mock object and a
>controller. You call the mock object, and then tell the
>controller what result it should return. I think the way you
>do this in python is a whole lot cleaner, but I miss being
>able to test for parameters.
>
>Cheers,
>
>- Michal   http://www.sabren.net/   sa...@ma...

I know the Python Mock module does not fit the definition of Mock Objects 
as given in the article by Tim MacKinnon & Steve Freeman 
(http://www.sidewize.com/company/mockobjects.pdf), since the Mock object 
does not do any verification of the calls made, but leaves that up to the 
caller.  I did think about adding some sort of internal checking, but since 
I didn't need it at the time I decided that YAGNI & DTSTTCPW applied and 
left it out.  It is possible to test the parameters of a specific method by 
subclassing the Mock class and adding that method, but if you have to do 
that for every method it negates the benefit of having the Mock class in 
the first place.

The biggest problem with the module as it stands is that it lets the user 
call any method on it, regardless of whether the call would be legal in the 
class being mocked.  It should be fairly easy to extend it to check this by 
initialising it with a list of legal method names (and perhaps their 
allowable parameters), but there is a danger of making the whole thing so 
complex to use that it becomes simpler to hand code a specific mock class 
from scratch.  I have just had a look at EasyMock, and it would be possible 
to do something similar to it in Python, passing in the class to be mocked 
and letting the Mock class extract all the legal methods and their 
parameters.   Perhaps one day I will get round to adding it...

Regards,

         Dave Kirby