patch-target 0.1.10

Description:

patchtarget 0.1.10

Patch Target: A tiny library for creating valid unittest.mock.patch target arguments
The ability to monkey patch modules, functions, classes, and class instances is a powerful part of testing Python code; however, the unittest.mock.patch
function depends on the developer providing a precise module path AS A STRING to the
object to be patched.
If you refactor where your modules live or make other changes, you will find the annoying and hard-to-decipher-at-first
errors pointing to an invalid module path string.
This small library, consisting of a single exported function,
attempts to make using this function a more straightforward, reliably correct experience.
the patch_target function takes 2 arguments:

a host_module of type ModuleType
and an object_to_be_patched, which can be of type Any,
but note that the only Patchable types are Named | str, where Named is a protocol describing any object with a __name__ attr
see note* on passing str types below

Since you're dealing with python objects instead of strings, you get more guarantees out of the box.
E.g. since you have to pass in a module instead of a string, that means you have to have successfully imported the module
into your test to begin with
example:
Given a src code file like this:
# myapp.mymodule.mysubmodule

import datetime
from uuid import uuid4

my_module_level_attribute = "some_value"

def get_current_time():
return datetime.datetime.now()

def generate_new_id():
return uuid4()

You can patch the non-deterministic pieces (current time and uuid generation) like so:
from unittest.mock import patch, Mock
from myapp.my_module import my_submodule # noqa
import datetime

import uuid

from patch_target import patch_target


# using the patch decorator to override a module imported into the host_module
@patch(patch_target(my_submodule, datetime)) # Using string paths the patch arg would be "myapp.mymodule.my_submodule.datetime"
def test_get_current_time(mock_datetime: Mock) -> None:
the_beginning_of_time = datetime.datetime(1970, 1, 1)
mock_datetime.datetime.now.return_value = the_beginning_of_time

actual = my_submodule.get_current_time()
expected = the_beginning_of_time

assert actual == expected


# using the patch context manager override a function imported into the host_module
def test_generate_new_id() -> None:
fake_id = "my-super-cool-id"
with patch(patch_target(my_submodule, uuid.uuid4)) as mock_uuid4: # Using string paths the patch arg would be "myapp.mymodule.my_submodule.uuid.uuid4"
mock_uuid4.return_value = fake_id

actual = my_submodule.generate_new_id()
expected = fake_id

assert actual == expected


# using the patch context manager override a module_attribute defined in the host_module
def test_get_module_level_attribute() -> None:
with patch(patch_target(my_submodule, "my_module_level_attribute"), "some_other_value"): # Using string paths the patch arg would be "myapp.mymodule.my_submodule.my_module_level_attribute"
actual = my_submodule.my_module_level_attribute
expected = "some_other_value"

assert actual == expected

* Note that though patching module-level attributes using the string name of the variable is supported, you can just use unittest.mock.patch.object the same way. So you don't need this lib to accomplish it.
# using unittest.mock.patch.object
from unittest.mock import patch

from myapp.my_module import my_submodule # noqa

def test_get_module_level_attribute() -> None:
with patch.object(my_submodule, "my_module_level_attribute", "some_other_value"): # Using string paths the patch arg would be "myapp.mymodule.my_submodule.my_module_level_attribute"
actual = my_submodule.my_module_level_attribute
expected = "some_other_value"

assert actual == expected