Context manager fixtures in PyTest - Test Execution Trace

Test Overview

This test uses a pytest fixture implemented as a context manager to set up and tear down a resource. It verifies that the resource is correctly initialized and cleaned up after the test.

Test Code - pytest

PyTest

import pytest

class Resource:
    def __init__(self):
        self.active = False
    def start(self):
        self.active = True
    def stop(self):
        self.active = False

@pytest.fixture
def resource():
    res = Resource()
    res.start()
    yield res
    res.stop()

def test_resource_active(resource):
    assert resource.active is True

Execution Trace - 8 Steps

Step	Action	System State	Assertion	Result
1	pytest starts test execution	pytest test runner initialized	-	PASS
2	pytest calls the 'resource' fixture before the test	Resource instance created with active = False	-	PASS
3	Resource.start() is called inside fixture, setting active = True	Resource active state is True	-	PASS
4	Fixture yields the resource instance to the test	Test receives resource with active = True	-	PASS
5	Test asserts resource.active is True	resource.active is True	assert resource.active is True	PASS
6	Test completes, pytest resumes fixture teardown	Resource active state still True	-	PASS
7	Resource.stop() is called in fixture teardown, setting active = False	Resource active state is False	-	PASS
8	pytest finishes test execution	All resources cleaned up	-	PASS

Failure Scenario

Failing Condition: Resource.start() is not called, so resource.active remains False

Execution Trace Quiz - 3 Questions

What does the fixture do before yielding the resource to the test?

A Calls res.stop() to deactivate the resource

B Does nothing before yielding

C Calls res.start() to activate the resource

D Raises an exception

Key Result

Using context manager style fixtures with yield in pytest helps ensure setup and cleanup happen reliably around tests.