Fixture finalization (request.addfinalizer) in PyTest

Introduction

We use fixture finalization to clean up after a test finishes. It helps keep tests independent and tidy by removing temporary data or closing resources.

When you create temporary files or folders during a test and want to delete them afterward.

When you open a database connection in a fixture and need to close it after the test.

When you start a server or service for testing and want to stop it after the test ends.

When you allocate resources like network sockets or hardware that must be released after use.

Syntax

PyTest

def fixture_name(request):
    # setup code here
    def cleanup():
        # cleanup code here
    request.addfinalizer(cleanup)
    return resource

The request parameter is a special pytest object that gives access to test context.

addfinalizer registers a function to run after the test using this fixture finishes.

Examples

This fixture creates a temporary file and ensures it is deleted after the test.

PyTest

import pytest

@pytest.fixture
def temp_file(request):
    filename = "temp.txt"
    with open(filename, "w") as f:
        f.write("hello")

    def cleanup():
        import os
        os.remove(filename)

    request.addfinalizer(cleanup)
    return filename

This fixture acquires a resource and releases it after the test using addfinalizer.

PyTest

import pytest

@pytest.fixture
def resource(request):
    res = acquire_resource()

    def cleanup():
        res.release()

    request.addfinalizer(cleanup)
    return res

Sample Program

This test uses a fixture that creates a list. After the test, the list is cleared by the finalizer. The print statements show the order of setup, test, and cleanup.

PyTest

import pytest

@pytest.fixture
def sample_list(request):
    data = [1, 2, 3]
    print("Setup: Created list")

    def cleanup():
        data.clear()
        print("Cleanup: Cleared list")

    request.addfinalizer(cleanup)
    return data

def test_modify_list(sample_list):
    sample_list.append(4)
    assert sample_list == [1, 2, 3, 4]
    print("Test: List modified")

Important Notes

Finalizers run even if the test fails, ensuring cleanup always happens.

You can add multiple finalizers if you need to clean up several things.

Using yield in fixtures is an alternative to addfinalizer for cleanup.

Summary

Fixture finalization cleans up resources after tests to keep tests independent.

request.addfinalizer registers cleanup functions to run after tests.

Finalizers run no matter if tests pass or fail, ensuring proper cleanup.