How to mock.patch a function with itself?

Question

I am trying to replace a function with itself, using different parameters.

Here is a sample. _{^{I can't share the real code, I'm on papery secrecy!}}

import unittest
from unittest.mock import patch

import mymodule
import production

class MyTest(unittest.TestCase):
    
    @patch('production.mymodule.myfunction', lambda: mymodule.myfunction(devmode=True))
    def test_main_with_mymodule_function_does_not_raise_exception(self):
        # This is an integration test. myfunction is used within main.
        try:
            production.main()
        except Exception as e:
            self.fail(e)

As expected the following generates a recursive call:

@patch('production_code.mymodule.myfunction', lambda: mymodule.myfunction(devmode=True))

We basically decorate myfunction with a decorator that will call myfunction. We get a nice "Too many recursions" exception!

I need a way to replace myfunction(devmode=False) with myfunction(devmode=True). But because I am in an integration test, and testing main(), I have no direct access to the function's parameters. Thing is, I made this very integration test to test how myfunction integrates with everything else in main.

Ideally, I shouldn't even have to create a devmode parameter, but I'm running a heavy sql query that requires to be limited by adding "TOP(10)" to the query.

Thanks for your help! :)

rdas · Accepted Answer · 2021-06-23 09:31:20Z

2

You can keep a reference to the unpatched function before your test runs. Use that in the patch call:

import unittest
from unittest.mock import patch


def iut(devmode=False):
    print(devmode)


class MyTest(unittest.TestCase):
    _unpatched = iut   # keep reference to unpatched IUT

    @patch('so_test.iut', lambda *args, **kwargs: MyTest._unpatched(devmode=True))
    def test(self):
        try:
            iut()
        except Exception as e:
            self.fail(e)

This results in the following, indicating devmode was set to True:

True

Note: you might need to pass args, kwargs to _unpatched depending in your function.

answered Jun 23, 2021 at 9:31

rdas

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