How to mock os.environ using pytest?

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I need to mock os.environ in unit tests written using the pytest framework.

Here is a dummy version of the code I want to test, located in getters.py:

import os

username = os.environ['MY_USER']
password = os.environ['MY_PASS']

def get_data(...):

    access_token = request_access_token(username, password)
    ...
    return data

and here is an example of a unit test in test_getters.py:

import pytest
import src.getters

class TestGetData(object):


    def test_something(self):

        data = src.getters.get_data(...)

        assert ...

Test collection fails with the following error:

=========================== short test summary info ============================
ERROR tests/test_getters.py - KeyError: 'MY_USER'
!!!!!!!!!!!!!!!!!!!! Interrupted: 1 error during collection !!!!!!!!!!!!!!!!!!!!
=============================== 1 error in 0.68s ===============================

I would like to be able to mock once for the whole test class if possible.

Is there some kind of a decorator I can use? Or some other recommended way of mocking os.environ?

pytest mocking unit-testing python
1 Answers

Use monkeypatch.setenv() of Monkeypatching:

Docs:

Modifying environment variables for a test e.g. to test program behavior if an environment variable is missing, or to set multiple values to a known variable. monkeypatch.setenv() and monkeypatch.delenv() can be used for these patches.

Code:

import pytest
import src.getters

class TestGetData(object):


    def test_something(self):
        monkeypatch.setenv('MY_USER', 'Nanna')
        monkeypatch.setenv('MY_PASS', 'P@ssw0rd')
        data = src.getters.get_data(...)

        assert ...
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