karlosss/pytest-override-env-var

Pytest mark to override a value of an environment variable.

pytest-override-env-var

Pytest mark to override a value of an environment variable.

The problem

Suppose we have the following function:

import os

def get_homedir() -> str:
    return os.environ["HOME"]

Now, we need to test it:

def test_get_homedir():
    assert get_homedir() == "/home/my_user"

This test will, though, succeed only if the username of the user is my_user. To make it succeed on all machines, we will need to patch the value of HOME environment variable:

import pytest

@pytest.mark.env(HOME="/home/test_user")
def test_get_homedir():
    assert get_homedir() == "/home/test_user"

Now, the test will pass, regardless of the username.

Installation

pip install pytest-override-env-var

After that, @pytest.mark.env(...) will "just work".

Supports Python 3.7+ and pytest 7+.

Examples

pytest-override-env-var resets the value of the variable after the test has finished:

def test_before():
    assert os.environ["HOME"] == "/home/my_user"

@pytest.mark.env(HOME="/home/test_user")
def test():
    assert os.environ["HOME"] == "/home/test_user"

def test_after():
    assert os.environ["HOME"] == "/home/my_user"

Multiple variables in one mark are supported:

@pytest.mark.env(A=1, B=2)
def test():
    assert os.environ["A"] == 1
    assert os.environ["B"] == 2

The env marks stack:

@pytest.mark.env(A=1)
@pytest.mark.env(B=2)
def test():
    assert os.environ["A"] == 1
    assert os.environ["B"] == 2

Upon redefinition, the innermost value is used:

@pytest.mark.env(A=1)
@pytest.mark.env(A=2)
def test():
    assert os.environ["A"] == 2

This can be useful in combination with classes:

@pytest.mark.env(A=1)
class TestSuite:
    def test_1(self):
        assert os.environ["A"] == 1
        
    @pytest.mark.env(A=2)
    def test_2(self):
        assert os.environ["A"] == 2

    def test_3(self):
        assert os.environ["A"] == 1

def test_outside():
    ...
    # A has the original value here

If the environment variable that is being patched is undefined, pytest-override-env-var will define it just for the test, and then delete it from the env again.