(Python Unit testing) Patch same object differently for different method in the same python file

Question

My python file has many methods defined in it. In many of the methods in the file, I am calling a function - let's say "fun1".

I want to mock the 'fun1' function for each of the methods differently. Is there a way to patch an object differently at method level and not at file level?

 Contents of aPythonFile.py
=======================================
    import fun from a_module

    def a():
        res= fun(aarg1, aarg2)
        return res

    def b():
        res = fun(barg1, barg2)
        return res

This came to my mind, as I know, the same "fun" can be patched differently for different files, then why not be able to patch differently based on the method in the file where it is called :-

@mock.patch("package.aPythonFile.fun") - Is Valid

@mock.patch("package.aPythonFile.a.fun") - ?? (possible?)
@mock.patch("package.aPythonFile.b.fun") - ?? (possible?)

This answer ( https://stackoverflow.com/questions/15753390/how-can-i-mock-requests-and-the-response) is not answering my question. What is suggested there is already known and followed by me. For my case, I want to organize the code more cleanly which this current approach (or the one referred as duplicate) is not providing! — VISHAL DAGA, Mar 19 '21 at 12:01
I am not sure what you are getting at. `@mock.patch` applies to an individual test method, so if you have a `test_a` and `test_b`, they can be patched with different methods. You do realize [one of the answers](https://stackoverflow.com/a/65437794) in that thread literally has the mocking done at the method level, you can just change the argument passed to `side_effect` to the method you specifically require for the specific test... — metatoaster, Mar 19 '21 at 12:46
It would then be useful to include how you are currently testing that `aPythonFile.py` of yours. Your edited code has only make your question even more confusing. You need to show _clearly_ what you are doing. If you want different return values for `fun1` that were called throughout an execution you may wish to refer to [this thread](https://stackoverflow.com/a/56191297/). In any case please clean up your question because as it is now is quite unclear on what you are asking, but at least you made it not obviously a duplicate of the other question, though as is it is still unanswerable. — metatoaster, Mar 19 '21 at 14:39
Ok thanks, I have edited it (hopefully its more clear). I am new with testing in python, but when I am learning about mock(ing) with inbuilt unit test, I feel that it is quite common that the object which is being mocked could be called several times in a file in practical scenario. I see that the module 'unittest.mock' allows an object to patch differently per file level in a package, then why not there is a way to patch an object, for example - able to patch it differently based on the method in which it is being in the file — VISHAL DAGA, Mar 19 '21 at 16:56
I am trying to architect a more manageable testing infrastructure for my team, and I wanted to have clear understanding if what i am asking is possible or not. I have searched through web and SO, but didn't find any information that clearly says if this is not possible — VISHAL DAGA, Mar 19 '21 at 17:01
It's possible. Mock the function with [side_effect](https://stackoverflow.com/a/7665754/362792) replacement function. Inside your side_effect function, get the function [name of caller](https://stackoverflow.com/a/900404/362792), then do different code based on which caller is it. Alternatively, instead of caller name you can vary behaviour based on argument values instead. — Hitobat, Mar 19 '21 at 18:29
It's more of a general programming question then, I too had thought about it. Somehow, I got lost in thinking that there could be a more standard way - 'mock' module way, but you comment gives me confidence there' no need... I think you could have had made your comment as an answer instead. As comment may not be obvious if someone else like me happens to have the same question... — VISHAL DAGA, Mar 19 '21 at 18:42

score 0 · Answer 1 · answered Mar 23 '21 at 06:17

Just provide different mock_fun.return_value for each test case.

E.g.

a_module.py:

def fun(a, b):
    pass

a_python_file.py:

from a_module import fun


def a():
    res = fun('a1', 'a2')
    return res


def b():
    res = fun('b1', 'b2')
    return res

test_a_python_file.py:

import unittest
from unittest import mock
from a_python_file import a, b


class TestAPythonFile(unittest.TestCase):
    @mock.patch('a_python_file.fun')
    def test_a(self, mock_fun):
        mock_fun.return_value = 'return value for a'
        actual = a()
        self.assertEqual(actual, 'return value for a')

    @mock.patch('a_python_file.fun')
    def test_b(self, mock_fun):
        mock_fun.return_value = 'return value for b'
        actual = b()
        self.assertEqual(actual, 'return value for b')


if __name__ == '__main__':
    unittest.main()

unit test result:

⚡  coverage run /Users/dulin/workspace/github.com/mrdulin/python-codelab/src/stackoverflow/66707457/test_a_python_file.py && coverage report -m --include='./src/**'  
..
----------------------------------------------------------------------
Ran 2 tests in 0.001s

OK
Name                                               Stmts   Miss  Cover   Missing
--------------------------------------------------------------------------------
src/stackoverflow/66707457/a_module.py                 2      1    50%   2
src/stackoverflow/66707457/a_python_file.py            7      0   100%
src/stackoverflow/66707457/test_a_python_file.py      16      0   100%
--------------------------------------------------------------------------------
TOTAL                                                 25      1    96%

(Python Unit testing) Patch same object differently for different method in the same python file

1 Answers1