[TIP] mocking out mixins and subclasses

[Nate Lowrie]

On 3/5/07, Michael Foord <fuzzyman at voidspace.org.uk> wrote:
> Nate Lowrie wrote:
> > I have several mixin classes that are subclassed by other classes.  I
> > am unit testing the mixin classes on there own. Some of the classes
> > that subclass these mixins call the mixin functions in some of the
> > methods.  I know that I can rebind the methods to mocked function
> > after I instantiate an object but there are some calls to the mixin
> > methods in the init section as well.  Ideally, I would like to mock
> > the mixin before creating any objects.
> >
> > How are other people handling unit testing for mixins and objects
> > using the mixin?  Is there an easy way to do this that I am
> > overlooking?
> >
> Hmm... mocking out base classes before instantiation is something I
> haven't had to do.
>
> As the code snippet below shows, you can do it by assigning to
> '__bases__', to swap out the base class.
>
>  >>> class x(object):
> ...  z = 3
> ...
>  >>> class y(object):
> ...  z = 6
> ...
>  >>> class z(x):
> ...  pass
> ...
>  >>> z.z
> 3
>  >>> z.__bases__
> (<class '__main__.x'>,)
>  >>> z.__bases__ = (y,)
>  >>> z.z
> 6
>
> So you should be able to swap out the base class before instantiating
> your object - this will work so long as the mixin methods are called
> using 'self'.

Thanks.  All of the mixin methods are being called with self.

>
> If the calls in init reference the class by name (rather than self),
> then you can just mock on the base class of course.
>
> HTH
>
> Fuzzyman
> http://www.voidspace.org.uk/python/index.shtml
>
> > Cheers,
> >
> > Nate L.
> >
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>
>