Fixture finalization (request.addfinalizer) in PyTest - Test Execution Trace

Test Overview

This test uses a pytest fixture with request.addfinalizer to run cleanup code after the test finishes. It verifies that the finalizer runs and changes a variable as expected.

Test Code - pytest

PyTest

import pytest

@pytest.fixture
def resource(request):
    state = {"cleaned": False}
    def cleanup():
        state["cleaned"] = True
    request.addfinalizer(cleanup)
    return state

def test_resource_cleanup(resource):
    assert resource["cleaned"] is False

# After test ends, finalizer sets resource["cleaned"] to True

Execution Trace - 7 Steps

Step	Action	System State	Assertion	Result
1	Test starts	pytest test runner initialized	-	PASS
2	Fixture 'resource' is called with 'request' parameter	Fixture creates state dictionary {'cleaned': False}	-	PASS
3	Fixture adds finalizer function 'cleanup' using request.addfinalizer	Finalizer registered to set state['cleaned'] = True after test	-	PASS
4	Test function 'test_resource_cleanup' runs with fixture 'resource'	state['cleaned'] is False at test start	Assert resource['cleaned'] is False	PASS
5	Test function completes	Test function finished without errors	-	PASS
6	pytest runs finalizer 'cleanup' registered by fixture	state['cleaned'] is set to True by finalizer	-	PASS
7	Test ends with all assertions passed and finalizer executed	Test environment cleaned up	-	PASS

Failure Scenario

Failing Condition: Finalizer function is not called or does not set 'cleaned' to True

Execution Trace Quiz - 3 Questions

What does request.addfinalizer do in this pytest fixture?

A Runs the cleanup function before the test starts

B Registers a cleanup function to run after the test finishes

C Skips the test if cleanup fails

D Runs the cleanup function during the test

Key Result

Using request.addfinalizer in pytest fixtures ensures cleanup code runs after tests, keeping tests isolated and preventing side effects.