Fixture finalization (request.addfinalizer) in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Understanding fixture finalization order with request.addfinalizer

What will be the output order of the print statements when running this pytest test?

PyTest

import pytest

def test_example(request):
    print("Start test")
    request.addfinalizer(lambda: print("First finalizer"))
    request.addfinalizer(lambda: print("Second finalizer"))
    print("End test")

A Start test\nEnd test\nFirst finalizer\nSecond finalizer

B First finalizer\nSecond finalizer\nStart test\nEnd test

C Start test\nEnd test\nSecond finalizer\nFirst finalizer

D Start test\nFirst finalizer\nEnd test\nSecond finalizer

💡 Hint

Remember that finalizers added later run first.

Pytest runs finalizers in reverse order of addition. So the last added finalizer runs first.

❓ assertion

intermediate

Correct assertion to verify finalizer execution

You want to test that a finalizer function was called after the test. Which assertion correctly verifies this?

PyTest

import pytest

called = []

def test_finalizer_called(request):
    def cleanup():
        called.append(True)
    request.addfinalizer(cleanup)
    assert ???

A called == []

B called == [True]

C called is None

D called == [False]

💡 Hint

Finalizers run after the test function finishes.

The finalizer runs after the test function completes, so during the test the list is still empty.

🔧 Debug

advanced

Identify the error in fixture finalizer usage

What error will this pytest fixture cause?

PyTest

import pytest

@pytest.fixture
def resource(request):
    print("Setup resource")
    request.addfinalizer("cleanup")
    return "resource"

A No error, runs fine

B TypeError: 'str' object is not callable

C NameError: name 'cleanup' is not defined

D SyntaxError: invalid syntax

💡 Hint

Check what type addfinalizer expects as argument.

addfinalizer expects a callable (function), but a string was passed, causing a TypeError.

🧠 Conceptual

advanced

Why use request.addfinalizer instead of yield in fixtures?

Which reason best explains when to prefer request.addfinalizer over yield in pytest fixtures?

A When you need multiple finalizers to run in a specific order

B When the fixture does not require any cleanup

C When you want to skip the test conditionally

D When you want to run cleanup code before the test starts

💡 Hint

Think about multiple cleanup steps and their order.

request.addfinalizer allows adding multiple cleanup functions that run in reverse order, which yield cannot do easily.

❓ framework

expert

Predict the final output of nested finalizers in pytest

Given this pytest test, what is the exact printed output?

PyTest

import pytest

def test_nested_finalizers(request):
    print("Test start")
    def first_cleanup():
        print("First cleanup start")
        def second_cleanup():
            print("Second cleanup")
        request.addfinalizer(second_cleanup)
        print("First cleanup end")
    request.addfinalizer(first_cleanup)
    print("Test end")

A Test start\nTest end\nFirst cleanup end\nFirst cleanup start\nSecond cleanup

B Test start\nTest end\nFirst cleanup start\nSecond cleanup\nFirst cleanup end

C Test start\nTest end\nSecond cleanup\nFirst cleanup start\nFirst cleanup end

D Test start\nTest end\nFirst cleanup start\nFirst cleanup end\nSecond cleanup

💡 Hint

Remember that finalizers run after the test, and added finalizers run in reverse order.

After the test ends, first_cleanup runs and adds second_cleanup as a finalizer. second_cleanup runs last.