monkeypatch fixture in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of monkeypatching a function

What is the output of the following pytest test when using the monkeypatch fixture?

PyTest

def get_data():
    return "original"

def test_monkeypatch(monkeypatch):
    def fake_get_data():
        return "patched"
    monkeypatch.setattr(__name__, "get_data", fake_get_data)
    result = get_data()
    print(result)

A original

B None

C patched

D Raises AttributeError

💡 Hint

Think about what monkeypatch.setattr does to the function get_data in the current module.

The monkeypatch fixture replaces the get_data function with fake_get_data, so calling get_data() returns 'patched'.

❓ assertion

intermediate

Correct assertion after monkeypatching an environment variable

Which assertion correctly verifies that the environment variable 'API_KEY' is patched to '12345' using monkeypatch?

PyTest

import os

def test_env(monkeypatch):
    monkeypatch.setenv('API_KEY', '12345')
    # Which assertion below is correct?

A assert os.environ.get('API_KEY') is None

B assert os.environ['API_KEY'] == '12345'

C assert monkeypatch.getenv('API_KEY') == '12345'

D assert os.getenv('API_KEY') == 12345

💡 Hint

Remember environment variables are strings and monkeypatch.setenv changes os.environ.

monkeypatch.setenv sets the environment variable as a string in os.environ, so assert os.environ['API_KEY'] == '12345' is correct.

🔧 Debug

advanced

Why does monkeypatch fail to patch a method?

Given the code below, why does monkeypatch.setattr fail to patch the method 'fetch' of class DataFetcher?

PyTest

class DataFetcher:
    def fetch(self):
        return "real data"

def test_fetch(monkeypatch):
    def fake_fetch(self):
        return "fake data"
    monkeypatch.setattr(DataFetcher, 'fetch', fake_fetch)
    fetcher = DataFetcher()
    result = fetcher.fetch()
    assert result == "fake data"

A The test will pass; monkeypatch correctly patches the method

B monkeypatch.setattr cannot patch class methods

C The fake_fetch method is missing the self parameter

D The fake_fetch method is not bound to the instance, causing a TypeError

💡 Hint

Check the method signature and how monkeypatch works on class methods.

The fake_fetch method correctly accepts self, so monkeypatch.setattr replaces fetch with fake_fetch. The test passes.

🧠 Conceptual

advanced

Scope of monkeypatch fixture in pytest

Which statement best describes the scope of changes made by the monkeypatch fixture in a pytest test?

A Changes made by monkeypatch affect only the imported modules, not local functions

B Changes made by monkeypatch persist across all tests in the module

C Changes made by monkeypatch require manual cleanup to revert

D Changes made by monkeypatch are reverted after the test function finishes

💡 Hint

Think about test isolation and cleanup in pytest.

monkeypatch automatically reverts changes after each test function to keep tests isolated.

❓ framework

expert

Using monkeypatch to mock a network call in pytest

You want to test a function that calls requests.get to fetch data from the internet. Which monkeypatch usage correctly mocks requests.get to return a response with status_code 200 and text 'mocked data'?

PyTest

import requests

def fetch_url(url):
    response = requests.get(url)
    return response.text

def test_fetch_url(monkeypatch):
    # Which option correctly mocks requests.get?

A

def fake_get(url):
    class Response:
        status_code = 200
        text = 'mocked data'
    return Response()
monkeypatch.setattr(requests, 'get', fake_get)

B monkeypatch.setattr(requests.get, 'return_value', {'status_code': 200, 'text': 'mocked data'})

C monkeypatch.setattr('requests.get', lambda url: {'status_code': 200, 'text': 'mocked data'})

D

def fake_get():
    return {'status_code': 200, 'text': 'mocked data'}
monkeypatch.setattr(requests, 'get', fake_get)

💡 Hint

requests.get returns a Response object, not a dictionary.

Option A defines a fake_get function returning an object with status_code and text attributes, matching requests.Response interface. This correctly mocks requests.get.