[TIP] pytest: mocking module imports

[Roy Wright]

Maybe use a delegate pattern instead of inheritance?  This would allow runtime binding of the parent.

Another thought is to put ClassY in a config file then dynamically resolve it for the ClassX definition. 

HTH

A free society is a single class society where everyone has the same rights.

On Apr 17, 2015, at 2:29 PM, Vinicius Kwiecien Ruoso <vinicius.ruoso at gmail.com> wrote:

> Sorry. The attachment follows.
> (and consider that test_classa_instance function does not have the
> mock_classB parameter at the second example).
> 
> 2015-04-17 16:23 GMT-03:00 Vinicius Kwiecien Ruoso <vinicius.ruoso at gmail.com>:
>> Hi!
>> 
>> Thanks for your answer. Unfortunately, this does not work for me.
>> libB is not importable during the test, and at some point the test try
>> to import it.
>> 
>> Let me show a real minimal example:
>> ├── src
>> │   └── mylib
>> │       ├── __init__.py
>> │       ├── liba.py
>> └── test
>>    └── mylib
>>        ├── conftest.py
>>        └── test_liba.py
>> 
>> 8<---------
>> <liba.py>
>> from mylibB.libb import ClassB
>> 
>> class ClassA(ClassB):
>>    pass
>> 
>> <conftest.py>
>> import os
>> import sys
>> 
>> _src_path = os.path.join(os.path.dirname(__file__), '..', '..', 'src')
>> sys.path.insert(0, os.path.abspath(_src_path))
>> 
>> <test_liba.py>
>> from mock import patch
>> 
>> @patch('mylibB.libb.ClassB')
>> def test_classa_instance(mock_classB):
>>    print mock_classB
>> 8<---------
>> 
>> This fails with: "ImportError: No module named mylibB" while executing
>> the patch code.
>> 
>> My real intent on the test_liba.py file was (and for that to work, I
>> need to mock libb module import at the conftest.py file):
>> 
>> import mylib.liba
>> 
>> def test_classa_instance(mock_classB):
>>    print mylib.liba.ClassA()
>> 
>> 
>> Attached you may find this file structure if you want to run it.
>> 
>> Just as a note, I'm using Python 2.6 right now. I intend to support
>> Python 2.7, but not 3.x at this time.
>> 
>> Thanks again!
>> Vinicius
>> 
>> 2015-04-17 14:47 GMT-03:00 Zhi An Ng <ngzhian at gmail.com>:
>>> Hi,
>>> I believe you can mock out ClassY as such:
>>> 
>>> @patch('liB.ClassY')
>>> def test_unit_test(self):
>>>    stuff
>>> 
>>> 
>>> More info:
>>> https://docs.python.org/3.3/library/unittest.mock.html#quick-guide
>>> 
>>> Best,
>>> Zhi An
>>> 
>>> On Fri, Apr 17, 2015 at 1:35 PM, Vinicius Kwiecien Ruoso
>>> <vinicius.ruoso at gmail.com> wrote:
>>>> 
>>>> Hi!
>>>> 
>>>> I've been using pytest and it is great. There is just one thing that
>>>> I'm not satisfied with the way I've implemented, that is module level
>>>> moking.
>>>> 
>>>> My scenario is as follows: libA and libB where libA depends on libB
>>>> (uses class definition as superclass). Let's assume this code:
>>>> 
>>>> <libA.py>
>>>> from libB import ClassY
>>>> 
>>>> class ClassX(ClassY):
>>>>   pass
>>>> 
>>>> <libB.py>
>>>> class ClassY(object):
>>>>   pass
>>>> 
>>>> Those modules live on different packages/repositories. LibB can be
>>>> unit tested just fine, but we need to mock libB module to allow libA
>>>> to be unit tested (libB won't be available in the moment of the test).
>>>> 
>>>> In a conftest.py file in the tests directory of libA, I've managed to
>>>> mock the module import by mocking sys.modules dictionary, but I did
>>>> this at the module (global) scope. I was not able to do it with any
>>>> hook (like pytest_configure), because the tests files are imported
>>>> before the hook is called. So a test_libA.py file with "import libA"
>>>> would cause the test to fail.
>>>> 
>>>> Am I doing something wrong or is this really the way to go?
>>>> 
>>>> Greetings,
>>>> Vinicius
>>>> 
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> <minimal-test.tar>
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