CODEWITHSUNDEEP
pythonmockingpython-unittestmonkeypatching
R T
R T

Reputation: 11

How to understand mock patching as it relates to import structures and what are alternatives?

I am having an issue where the patch method from the unittest.mock module is only working when I patch attributes of imported modules in other files. I do not understand if this is an issue of my import patterns or a misunderstanding of how patching works. (I am importing the app code before the patch is able to run).

I devised a test to show how the functionality is confusing me:

In my app code I have the following code

from datetime import date
...
import boto3
...
from common.functions import asodates2datetime
from core.mixins.usecases import ASOUsecaseTools


class foo:
    @staticmethod
    @ASOUsecaseTools.get_by_name
    def bar(self, relevant_date):
        client = boto3.client("s3")
        today = date.today()
        date = asodates2datetime(relevant_date)

And from my test code I can patch in the following way:

@mock.patch("src.aoi.usecases.date")
@mock.patch("src.aoi.usecases.ASOUsecaseTools.get_by_name")
@mock.patch("src.aoi.usecases.asodates2datetime")
@mock.patch("src.aoi.usecases.boto3.client")
def test_foo_gets_bar(self, m_d, m_g, m_a, m_c):
    m_d.today.return_value = <date>
    m_d.side_effect = lambda *args, **kw: date(*args, **kw)
    # more patching of functions here

However, when the test is run, If I set a breakpoint in the bar function and check the value of the patched items, only the patched methods show up as MagicMock

>>> boto3.client
    <MagicMock name='client...>
>>> ASOUsecaseTools.get_by_name
    <MagicMock name='get_by_name...>
>>> asodates2datetime
    <function asodates2datetime...>
>>> date
    <class 'datetime.date'>

The thing that confuses me is that I am patching along with how the docs say to patch: https://docs.python.org/3/library/unittest.mock-examples.html#partial-mocking

Also the fact that patched methods work but classes and functions don't indicates that the import structure is not a problem because the imported methods would be overwritten in the same way as the imported classes. It also indicates that the import paths are not incorrect; as the only difference between the patches is the type of object they are patching.

My current workaround is using the freeze package to freeze the date, but I prefer using builtin packages if possible.

Upvotes: 0

Views: 24

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