monkeypatch.setenv in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does monkeypatch.setenv do in pytest?

monkeypatch.setenv temporarily sets or changes an environment variable during a test. It helps simulate different environment settings without affecting the real system environment.

beginner

How do you use monkeypatch.setenv to set an environment variable named API_KEY to 12345?

<pre>import os

def test_api_key(monkeypatch):
    monkeypatch.setenv('API_KEY', '12345')
    assert os.getenv('API_KEY') == '12345'</pre>

intermediate

Why is it better to use monkeypatch.setenv instead of directly modifying os.environ in tests?

Using monkeypatch.setenv ensures the environment variable changes are temporary and automatically reverted after the test. Directly modifying os.environ can cause side effects on other tests.

beginner

What happens to environment variables set by monkeypatch.setenv after the test finishes?

They are automatically restored to their original values or removed if they did not exist before. This keeps tests isolated and prevents side effects.

intermediate

Can monkeypatch.setenv be used to unset an environment variable? How?

Yes. You can unset an environment variable by setting its value to None with monkeypatch.setenv('VAR_NAME', None). This removes the variable for the test duration.

What is the main purpose of monkeypatch.setenv in pytest?

A Create new files for testing

B Permanently change environment variables on the system

C Mock HTTP requests

D Temporarily change environment variables during a test

monkeypatch.setenv only changes environment variables temporarily during a test, not permanently.

After a test using monkeypatch.setenv finishes, what happens to the environment variables?

A They are restored to their original state

B They remain changed permanently

C They are deleted from the system

D They cause the test to fail

Environment variables are restored to their original values to keep tests isolated.

Which of the following is a correct way to set an environment variable DEBUG to true using monkeypatch?

A monkeypatch.setenv('DEBUG', 'true')

B monkeypatch.setenv(DEBUG=true)

C os.environ['DEBUG'] = true

D monkeypatch.setenv('DEBUG')

Option A correctly sets the variable as a string value using monkeypatch.

Why should you prefer monkeypatch.setenv over modifying os.environ directly in tests?

A It is faster

B It requires less code

C It automatically cleans up changes after tests

D It works only on Windows

monkeypatch ensures environment changes are temporary and cleaned up after tests.

How do you remove an environment variable PATH temporarily in a pytest test?

A monkeypatch.delenv('PATH')

B monkeypatch.setenv('PATH', None)

C os.environ.pop('PATH')

D monkeypatch.setenv('PATH', '')

Setting the variable to None with monkeypatch.setenv removes it temporarily.

Explain how monkeypatch.setenv helps keep tests isolated and why this is important.

Think about what happens if environment variables stay changed after a test.

Describe a simple pytest test example using monkeypatch.setenv to simulate an environment variable and verify it.

Show how to set and check an environment variable inside a test.