Need to mock out some base class behavior in a python test case

Question

My title is fairly descriptive, but here goes. Suppose I have this setup.

class BaseClass(object):
    def __init__(self):
        pass
    def base_function(self, param="Hello World"):
        print param

#multiple inheritance probably irrelevant but my problem deals with it
class DerivedClass(BaseClass, AnotherBaseClass):
    def __init__(self):
        pass
    def advanced_function(self):
        #blah blah blah
        #code code code
        self.base_function()

Now, I have a situation where I am testing a derived class, but in doing so, I need to ensure that it's base class methods are called. I tried doing something like this

from mock import MagicMock

d = DerivedClass()
super(DerivedClass, d).base_function = MagicMock()
d.advanced_function()
super(DerivedClass, d).base_function.assert_called()

I'm 100% sure this setup is wrong, because

AttributeError: 'super' object has no attribute 'base_function'

I know I'm doing something wrong with super, anyone have an idea?

Have you tried accessing BaseClass.base_function directly, rather than via super? — jonrsharpe
– jonrsharpe, Commented Dec 11, 2013 at 22:11
This works. Why? I thought I needed to use a specific instance of the class. How does setting BaseClass.base_function to equal MagicMock make all derived instances mocked out as well? If you have a link to read explaining all this, much appreciated. — Zack
– Zack, Commented Dec 11, 2013 at 22:17

jonrsharpe · Accepted Answer · 2013-12-11 22:28:06Z

1

Access via BaseClass.base_function. As you don't overload the method, you just inherit it, the DerivedClass.base_function is the same object:

id(BaseClass.base_function) == id(DerivedClass.base_function)

When the instances are created, they inherit the mock.

answered Dec 11, 2013 at 22:28

jonrsharpe

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