monkeypatch.setattr in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of monkeypatch.setattr on a function attribute

What will be the output of this pytest test function when monkeypatch.setattr is used to replace a function?

PyTest

def greet():
    return "Hello"

def test_greet(monkeypatch):
    def fake_greet():
        return "Hi"
    monkeypatch.setattr(__name__, "greet", fake_greet)
    result = greet()
    print(result)

A Hi

B Hello

C AttributeError

D TypeError

💡 Hint

Think about what monkeypatch.setattr does to the function greet inside the test.

monkeypatch.setattr replaces the greet function with fake_greet during the test, so calling greet() returns 'Hi'.

❓ assertion

intermediate

Correct assertion after monkeypatch.setattr on an object attribute

Given this code, which assertion correctly verifies the monkeypatched attribute value?

PyTest

class User:
    active = True

def test_user_active(monkeypatch):
    monkeypatch.setattr(User, "active", False)
    user = User()
    # Which assertion is correct here?

A assert user.active is False

B assert User.active is True

C assert user.active is True

D assert User.active is None

💡 Hint

monkeypatch.setattr changes the attribute value on the class User.

monkeypatch.setattr sets User.active to False, so user.active will also be False.

🔧 Debug

advanced

Identify the error in monkeypatch.setattr usage

What error will this test raise when run with pytest?

PyTest

def test_patch(monkeypatch):
    import os
    monkeypatch.setattr(os.path, "exists", lambda x: True)
    print(os.path.exists("anyfile.txt"))

A NameError: name 'os' is not defined

B Prints True

C TypeError: setattr() arg 1 must be module, class, or instance

D AttributeError: module 'os' has no attribute 'path'

💡 Hint

Check the first argument to monkeypatch.setattr and what it expects.

monkeypatch.setattr expects a module, class, or instance as first argument, not a string.

🧠 Conceptual

advanced

Understanding monkeypatch.setattr scope and cleanup

Which statement about monkeypatch.setattr is TRUE regarding its effect and cleanup?

A Changes made by monkeypatch.setattr persist after the test finishes

B monkeypatch.setattr permanently deletes the original attribute

C monkeypatch.setattr only affects the patched attribute during the test and reverts after

D monkeypatch.setattr requires manual cleanup to restore original attributes

💡 Hint

Think about test isolation and why monkeypatch is useful.

monkeypatch.setattr automatically reverts changes after the test to keep tests isolated.

❓ framework

expert

Best practice for monkeypatching a method in a class instance

You want to monkeypatch the method 'calculate' of an instance 'obj' of class 'Calculator' during a pytest test. Which code snippet correctly patches the method only for this test?

PyTest

class Calculator:
    def calculate(self, x):
        return x * 2

def test_calculate(monkeypatch):
    obj = Calculator()
    # Which monkeypatch code is correct here?

A monkeypatch.setattr(obj.calculate, lambda x: 42)

B monkeypatch.setattr(Calculator, "calculate", lambda self, x: 42)

C monkeypatch.setattr("Calculator", "calculate", lambda self, x: 42)

D monkeypatch.setattr(obj, "calculate", lambda x: 42)

💡 Hint

Remember monkeypatch.setattr needs the object and attribute name as separate arguments.

To patch a method on an instance, pass the instance and method name as arguments, then the replacement function.