[TIP] Unit testing functions which call super

Marcin Tustin Marcin.Tustin at dealertrack.com
Wed Aug 13 13:10:42 PDT 2014

Yes, that’s valid, but the problem (which I guess I didn’t specify) is that the base classes are both numerous and may be indirect. I don’t want to have to update static patch lists in tests every time a base class changes. This is a large, and evolving, codebase.

From: testing-in-python-bounces at lists.idyll.org [mailto:testing-in-python-bounces at lists.idyll.org] On Behalf Of Harry Percival
Sent: Wednesday, August 13, 2014 2:23 PM
To: Harry Percival
Cc: testing-in-python at lists.idyll.org
Subject: Re: [TIP] Unit testing functions which call super

Like this? https://gist.github.com/hjwp/44210e3e164bbb1fed18

On 13 August 2014 19:11, Harry Percival <harry.percival at gmail.com<mailto:harry.percival at gmail.com>> wrote:
If you know what the parent class is in advance, could you use mock.patch to stub out the parent method?

On 13 August 2014 19:00, Marcin Tustin <Marcin.Tustin at dealertrack.com<mailto:Marcin.Tustin at dealertrack.com>> wrote:
Hi All,

I’ve come across a method which I needed to add a unit test for, which calls super, e.g.

def foofunc(self):
    x= do_some_stuff()
    if x:
        return x
    return super(WhatevClass, self).foofunc()

Now, I don’t want to integration test the whole stack of super foofunc methods, just unit test that one, down to the super call.

I’ve accomplished this with, in my test (excuse the 8 leading spaces):

def setUp(self):
        self.method_archive = {}
        for klass in WhatevClass.__mro__[1:]:
            # we use the class as its own sentinel
            meth_or_klass = klass.__dict__.get('foofunc', klass)
            if meth_or_klass != klass:
                self.method_archive[klass] = meth_or_klass
                del klass.foofunc
        # now patch an arbitrary member of the mro to supply a dummy foofunc
        self.sentinel_klass = next(iter(self.method_archive))
        self.mock_sentinel = mock.MagicMock()
        self.sentinel_klass.foofunc = self.mock_sentinel

And corresponding unpatching in tearDown.

Is there any other approach which is standard, or objectively better?


Marcin Tustin
Senior Software Engineer

1111 Marcus Avenue
Lake Success, NY 11042
p 516.300.7072

dealertrack technologies™

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Harry J.W. Percival
Twitter: @hjwp
Mobile:  +44 (0) 78877 02511
Skype:         harry.percival

Harry J.W. Percival
Twitter: @hjwp
Mobile:  +44 (0) 78877 02511
Skype:         harry.percival
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