monkeypatch fixture in PyTest - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the monkeypatch fixture in pytest?

The monkeypatch fixture allows you to safely modify or replace attributes, dictionaries, environment variables, or functions during a test, without affecting other tests.

beginner

How do you use monkeypatch to change an environment variable in a test?

Use monkeypatch.setenv('VAR_NAME', 'value') to set or change an environment variable temporarily during the test.

beginner

What happens to changes made by monkeypatch after the test finishes?

All changes made by monkeypatch are automatically undone after the test, restoring the original state to avoid side effects on other tests.

intermediate

Show an example of using monkeypatch to replace a function during a test.

Example:<br><pre>def fake_func():
    return 'fake'

import module

def test_func(monkeypatch):
    monkeypatch.setattr(module, 'func', fake_func)
    assert module.func() == 'fake'</pre>

intermediate

Why is monkeypatch preferred over directly modifying global variables or functions in tests?

Because monkeypatch safely isolates changes to the test scope and automatically reverts them, preventing unexpected side effects and making tests more reliable.

What does monkeypatch.setattr() do in pytest?

A Runs a test multiple times

B Replaces an attribute or function temporarily during a test

C Permanently changes a function in the codebase

D Skips a test

monkeypatch.setattr() temporarily replaces an attribute or function only during the test, then restores it after.

How does monkeypatch affect environment variables during a test?

A It permanently changes them

B It copies environment variables to a file

C It ignores environment variables

D It temporarily sets or deletes them for the test duration

monkeypatch.setenv() and monkeypatch.delenv() temporarily modify environment variables only during the test.

What happens if you forget to use monkeypatch and modify globals directly in tests?

A Other tests may fail due to leftover changes

B Tests run faster

C Nothing, tests are isolated automatically

D The test framework will fix it

Direct global changes can cause side effects, making other tests fail unpredictably.

Which of these is NOT a feature of monkeypatch?

A Temporarily replace functions or attributes

B Modify environment variables temporarily

C Automatically generate test data

D Automatically undo changes after test

monkeypatch does not generate test data; it only modifies code or environment temporarily.

How do you use monkeypatch in a pytest test function?

A Add <code>monkeypatch</code> as a parameter to the test function

B Import and call <code>monkeypatch()</code> inside the test

C Use a decorator <code>@monkeypatch</code>

D Call <code>pytest.monkeypatch()</code> globally

pytest injects the monkeypatch fixture when you add it as a parameter to your test function.

Explain how the monkeypatch fixture helps keep tests isolated and reliable.

Think about how changing something only during a test helps avoid problems.

Describe a scenario where you would use monkeypatch.setattr() in a test.

Imagine you want to test code that calls a function you can't or don't want to run.