Fixture finalization (request.addfinalizer) in PyTest - Build an Automation Script

Verify resource cleanup using pytest fixture finalizer

Preconditions (2)

Step 1: Create a pytest fixture that sets up a resource (e.g., opens a file or creates a list)

Step 2: Use request.addfinalizer inside the fixture to add a cleanup function that releases the resource

Step 3: Write a test function that uses this fixture

Step 4: Run the test

Step 5: Verify that the cleanup function runs after the test completes

✅ Expected Result: The test passes and the cleanup function is executed after the test, releasing the resource properly

Automation Requirements - pytest

Assertions Needed:

Assert the resource is set up correctly in the fixture

Assert the cleanup function is called after the test

Best Practices:

Use request.addfinalizer to register cleanup functions

Keep setup and teardown logic inside fixtures

Avoid side effects outside fixtures

Use assert statements for validation

Automated Solution

PyTest

import pytest

class Resource:
    def __init__(self):
        self.active = False
    def open(self):
        self.active = True
    def close(self):
        self.active = False

@pytest.fixture
def resource_fixture(request):
    res = Resource()
    res.open()

    def cleanup():
        res.close()
        print("Cleanup called: resource closed")

    request.addfinalizer(cleanup)
    return res

def test_resource_usage(resource_fixture):
    # Assert resource is active during test
    assert resource_fixture.active is True

    # The cleanup will run after this test finishes

This code defines a Resource class to simulate a resource that can be opened and closed.

The resource_fixture fixture creates and opens the resource. It uses request.addfinalizer to register a cleanup function that closes the resource after the test finishes.

The test test_resource_usage uses the fixture and asserts the resource is active during the test.

After the test completes, pytest automatically calls the cleanup function to close the resource, ensuring proper cleanup.

Common Mistakes - 3 Pitfalls

Not using request.addfinalizer and instead trying to cleanup inside the test

Forgetting to call the cleanup function inside addfinalizer

Modifying shared state in cleanup without isolation

Bonus Challenge

Now add a second fixture that depends on the first fixture and also uses addfinalizer for cleanup

Show Hint

Practice

1. What is the main purpose of using request.addfinalizer in a pytest fixture?

easy

A. To register a cleanup function that runs after the test finishes

B. To skip the test if a condition is met

C. To mark a test as expected to fail

D. To parametrize the test with multiple inputs

Solution

1. Step 1: Understand the role of request.addfinalizer

   This method is used inside fixtures to add a function that will run after the test, regardless of test outcome.

2. Step 2: Identify the purpose of finalizers

   Finalizers clean up resources like files, connections, or data to keep tests independent and avoid side effects.

3. Final Answer:

   To register a cleanup function that runs after the test finishes -> Option A

4. Quick Check:

   Finalizer = cleanup function [OK]

Hint: Finalizers always clean up after tests finish [OK]

Common Mistakes:

• Confusing finalizers with test skipping
• Thinking finalizers run before tests
• Using finalizers to parametrize tests

2. Which of the following is the correct syntax to add a finalizer inside a pytest fixture using request?

easy

A. request.addfinalizer(cleanup_function())

B. request.addfinalizer(cleanup_function)

C. request.addfinalizer = cleanup_function

D. request.finalizer(cleanup_function)

Solution

1. Step 1: Recall the correct method call syntax

   The addfinalizer method expects a callable (function) without calling it immediately.

2. Step 2: Analyze each option

   request.addfinalizer(cleanup_function()) calls the function immediately, which is incorrect. request.addfinalizer(cleanup_function) passes the function reference correctly. Options C and D use invalid syntax.

3. Final Answer:

   request.addfinalizer(cleanup_function) -> Option B

4. Quick Check:

   Pass function, don't call it [OK]

Hint: Pass function name without parentheses to addfinalizer [OK]

Common Mistakes:

• Calling the cleanup function immediately
• Assigning instead of calling addfinalizer
• Using wrong method names

3. What will be the output when running this pytest code snippet?

import pytest

def cleanup():
    print('Cleanup done')

@pytest.fixture
def resource(request):
    request.addfinalizer(cleanup)
    print('Setup done')
    return 42

def test_example(resource):
    print(f'Test got resource: {resource}')
    assert resource == 42

medium

A. Cleanup done\nSetup done\nTest got resource: 42

B. Setup done\nCleanup done\nTest got resource: 42

C. Test got resource: 42\nSetup done\nCleanup done

D. Setup done\nTest got resource: 42\nCleanup done

Solution

1. Step 1: Trace the fixture and test execution order

   Fixture runs first, printing 'Setup done'. Then test runs, printing 'Test got resource: 42'. After test finishes, finalizer runs printing 'Cleanup done'.

2. Step 2: Match output order with options

   Only Setup done\nTest got resource: 42\nCleanup done matches the order: setup, test, cleanup.

3. Final Answer:

   Setup done\nTest got resource: 42\nCleanup done -> Option D

4. Quick Check:

   Setup -> Test -> Cleanup order [OK]

Hint: Finalizer runs after test, not before or during [OK]

Common Mistakes:

• Assuming cleanup runs before test
• Mixing print order of setup and test
• Thinking finalizer runs during fixture setup

4. Identify the error in this pytest fixture code that uses request.addfinalizer:

@pytest.fixture
def my_fixture(request):
    def cleanup():
        print('Cleaning up')
    request.addfinalizer(cleanup())
    return 'data'

medium

A. The cleanup function must be defined outside the fixture

B. The fixture should not return any value

C. The cleanup function is called immediately instead of being passed

D. The addfinalizer method does not exist on request

Solution

1. Step 1: Check how cleanup is passed to addfinalizer

   The code calls cleanup() immediately, passing its result (None) instead of the function itself.

2. Step 2: Understand correct usage

   We must pass the function reference without parentheses to addfinalizer so it runs after the test.

3. Final Answer:

   The cleanup function is called immediately instead of being passed -> Option C

4. Quick Check:

   Pass function, don't call it [OK]

Hint: Don't add parentheses when passing cleanup to addfinalizer [OK]

Common Mistakes:

• Calling cleanup instead of passing it
• Defining cleanup outside fixture unnecessarily
• Thinking addfinalizer is not a method

5. You want to use request.addfinalizer to close two resources after a test. Which code correctly ensures both cleanup functions run after the test?

hard

A. @pytest.fixture
def multi_resource(request):
def cleanup1():
print('Close resource 1')
def cleanup2():
print('Close resource 2')
request.addfinalizer(cleanup1)
request.addfinalizer(cleanup2)
return 'resources'

B. @pytest.fixture
def multi_resource(request):
def cleanup():
print('Close resource 1')
print('Close resource 2')
request.addfinalizer(cleanup())
return 'resources'

C. @pytest.fixture
def multi_resource(request):
def cleanup1():
print('Close resource 1')
def cleanup2():
print('Close resource 2')
request.addfinalizer(cleanup1())
request.addfinalizer(cleanup2())
return 'resources'

D. @pytest.fixture
def multi_resource(request):
def cleanup1():
print('Close resource 1')
def cleanup2():
print('Close resource 2')
request.addfinalizer = cleanup1
request.addfinalizer = cleanup2
return 'resources'

Solution

1. Step 1: Check how finalizers are registered

   @pytest.fixture
   def multi_resource(request):
       def cleanup1():
           print('Close resource 1')
       def cleanup2():
           print('Close resource 2')
       request.addfinalizer(cleanup1)
       request.addfinalizer(cleanup2)
       return 'resources'

   correctly calls request.addfinalizer twice, passing function references without calling them.

2. Step 2: Identify errors in other options

   @pytest.fixture
   def multi_resource(request):
       def cleanup():
           print('Close resource 1')
           print('Close resource 2')
       request.addfinalizer(cleanup())
       return 'resources'

   calls cleanup immediately (wrong).

   @pytest.fixture
   def multi_resource(request):
       def cleanup1():
           print('Close resource 1')
       def cleanup2():
           print('Close resource 2')
       request.addfinalizer(cleanup1())
       request.addfinalizer(cleanup2())
       return 'resources'

   calls cleanup1() and cleanup2() immediately (wrong).

   @pytest.fixture
   def multi_resource(request):
       def cleanup1():
           print('Close resource 1')
       def cleanup2():
           print('Close resource 2')
       request.addfinalizer = cleanup1
       request.addfinalizer = cleanup2
       return 'resources'

   assigns functions to request.addfinalizer attribute, overwriting it (wrong).

3. Final Answer:

   Option A correctly registers both cleanup functions as finalizers -> Option A

4. Quick Check:

   Call addfinalizer twice with function references [OK]

Hint: Call addfinalizer separately for each cleanup function [OK]

Common Mistakes:

• Calling cleanup functions immediately
• Overwriting addfinalizer instead of calling it
• Combining cleanup prints but calling immediately