monkeypatch.setenv in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output after monkeypatch.setenv changes the environment variable?

Consider this pytest test function that uses monkeypatch.setenv to change an environment variable. What will be printed when the test runs?

PyTest

import os

def test_env(monkeypatch):
    monkeypatch.setenv('MY_VAR', '123')
    print(os.getenv('MY_VAR'))

A None

B 123

C MY_VAR

D '' (empty string)

💡 Hint

Remember that monkeypatch.setenv temporarily sets environment variables during the test.

The monkeypatch.setenv function sets the environment variable 'MY_VAR' to '123' for the duration of the test. So os.getenv('MY_VAR') returns '123'.

❓ assertion

intermediate

Which assertion correctly verifies the environment variable set by monkeypatch.setenv?

You want to check that the environment variable 'API_KEY' is set to 'secret' inside a pytest test using monkeypatch. Which assertion is correct?

A assert os.getenv('API_KEY') is not None

B assert os.environ['API_KEY'] == 'secret'

C assert os.getenv('API_KEY') == 'secret'

D assert monkeypatch.getenv('API_KEY') == 'secret'

💡 Hint

Use the standard way to get environment variables in Python.

The correct way is to use os.getenv('API_KEY') and compare it to 'secret'. Option C can raise KeyError if 'API_KEY' is missing. Option C is invalid because monkeypatch does not have a getenv method. Option C only checks presence, not value.

🔧 Debug

advanced

Why does this test fail to see the environment variable set by monkeypatch.setenv?

This pytest test tries to set 'CONFIG' environment variable but fails to see it inside the tested function. Why?

import os

config_cache = os.getenv('CONFIG')

def get_config():
    return config_cache

def test_config(monkeypatch):
    monkeypatch.setenv('CONFIG', 'value')
    assert get_config() == 'value'

A The get_config function caches the environment variable before the test

B The environment variable is not set globally, so get_config cannot see it

C The test is missing monkeypatch.delenv('CONFIG') before setting it

D The get_config function is called before monkeypatch.setenv runs

💡 Hint

Think about when environment variables are read and if caching can affect the test.

If get_config reads and caches the environment variable before the test runs, monkeypatch.setenv will not affect the cached value. This causes the test to fail.

❓ framework

advanced

How does monkeypatch.setenv affect environment variables during pytest test execution?

Which statement best describes the behavior of monkeypatch.setenv in pytest?

A It temporarily sets the environment variable only during the test and restores it after

B It sets the environment variable only for subprocesses spawned by the test

C It sets the environment variable only if it does not already exist

D It permanently changes the environment variable for the whole system

💡 Hint

Think about test isolation and cleanup.

monkeypatch.setenv temporarily sets environment variables during the test and restores the original environment after the test finishes, ensuring no side effects.

🧠 Conceptual

expert

What is the correct way to test code that reads environment variables using monkeypatch.setenv and pytest?

You have a function that reads an environment variable 'MODE'. You want to test it with different values using pytest and monkeypatch. Which approach is best?

A Pass the environment variable as a function argument instead of reading it inside the function

B Set the environment variable globally before running pytest and do not use monkeypatch

C Modify os.environ directly without monkeypatch to set 'MODE' before each test

D Use monkeypatch.setenv('MODE', value) inside each test to set the variable, then call the function

💡 Hint

Consider test isolation and avoiding side effects.

Using monkeypatch.setenv inside each test ensures environment variables are set temporarily and isolated per test, avoiding side effects and making tests reliable.