Samples of monkeypatching with Pytest

test_monkeypatching.py

import os
import time

import pytest


ENV_VAR_NAME = "DUMMY_VAR"
os.environ["CUSTOM_VAR"] = "Unchanged"
my_dict = {"a": 11, "b": 22}


class MockClass:
    attribute1 = 1
    attribute2 = 2


def test_monkeypatch_environmentals(monkeypatch):
    assert "DUMMY_VAR" not in os.environ
    monkeypatch.setenv(ENV_VAR_NAME, "123")
    monkeypatch.setenv("CUSTOM_VAR", "Changed")
    assert os.environ[ENV_VAR_NAME] == "123"
    assert os.environ["CUSTOM_VAR"] == "Changed"


def test_monkeypatch_function(monkeypatch):
    monkeypatch.setattr(time, "time", lambda: 12345)
    assert time.time() == 12345
    assert time.time() == 12345


def test_monkeypatch_delete_attribute(monkeypatch):
    instance1 = MockClass()
    monkeypatch.delattr(MockClass, "attribute2")

    assert instance1.attribute1 == 1
    with pytest.raises(AttributeError):
        assert instance1.attribute2 == 2


def test_monkeypatch_dicts(monkeypatch):
    monkeypatch.setitem(my_dict, "c", 33)
    monkeypatch.delitem(my_dict, "b")
    assert my_dict == {"a": 11, "c": 33}


def test_unpatching_works():
    assert ENV_VAR_NAME not in os.environ
    assert os.environ["CUSTOM_VAR"] == "Unchanged"
    assert MockClass().attribute2 == 2
    assert my_dict == {"a": 11, "b": 22}