[Python] Setting os.environ["TMP"] works in the code but not in pytest tests

I have the following python code:

import tempfile
import os

def test_paul_confused():
os.environ["TMP"] = "/home/fedora"
assert tempfile.gettempdir() == "/home/fedora"
print(tempfile.gettempdir())

test_paul_confused()


When I run this code from the command line I get the expected result:

(fedora) [fedora@ip-10-254-6-135 ~]$ uv run pytest.py
/home/fedora


However when I run the code via pytest, the TMP directory doesn't get set correctly!

(fedora) [fedora@ip-10-254-6-135 ~]$ uv run pytest pytest.py
============================ test session starts =============================
platform linux -- Python 3.13.5, pytest-8.4.1, pluggy-1.6.0
rootdir: /home/fedora
collected 0 items / 1 error

=================================== ERRORS ===================================
_________________________ ERROR collecting pytest.py _________________________
pytest.py:9: in <module>
test_paul_confused()
pytest.py:6: in test_paul_confused
assert tempfile.gettempdir() == "/home/fedora"
E AssertionError: assert '/tmp' == '/home/fedora'
E + where '/tmp' = <function gettempdir at 0xffffb3d83d80>()
E + where <function gettempdir at 0xffffb3d83d80> = tempfile.gettempdir
========================== short test summary info ===========================
ERROR pytest.py - AssertionError: assert '/tmp' == '/home/fedora'
!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!
============================== 1 error in 0.07s ==============================
(fedora) [fedora@ip-10-254-6-135 ~]$


Why is this code behaving differently in testing than when it's run outside of testing?

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