[Python] Pytest: Patch a global variable

How do you patch a variable with mock or pytest-mock. Assume the variable is defined in another python script and is used by many other scripts. I would like to mock it within pytest_cmdline_main so that all the scripts using that variable will be mocked accordingly.

A quick example will be

in env.py


VAR = "something"

in conftest.py


import os
import sys
from unittest.mock import patch


TEST_DIR = os.path.dirname(os.path.realpath(__file__))


class MockThings():
def __init__(self):
self.setup()

def setup(self):
mock_var = patch('env.VAR').start()
mock_var.return_value = "updated"


def pytest_cmdline_main(config):
sys.path.append(TEST_DIR)
MockThings()

in test_something.py


from env import VAR


def test_sample():
print(VAR)
# do something else here
assert False

def test_sample2():
print(VAR)
# do something else here
assert False


When you run pytest -v

The test will fail as expected, but under the stdout it will state something like: <MagicMock name='VAR' id='140102687826416'>

Because it is treating the mock as a function, if I replace the print(VAR) with print(VAR()) then the print out will be correct (updated).

How do I mock this variable, and not treat it as a function? I know you can just set VAR="updated" in the test function itself, but I just want it mocked and I guess this is not a great representation of my actual use case, but I just wanted to have a quick simple test code you can run and understand easily.

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