Fixture scope with parallel tests in PyTest - Test Execution Trace

Test Overview

This test demonstrates how a pytest fixture with module scope behaves when running tests in parallel. It verifies that the fixture is created once per module and shared across parallel test functions.

Test Code - pytest

PyTest

import pytest

@pytest.fixture(scope="module")
def resource():
    print("Setup resource")
    yield "resource_data"
    print("Teardown resource")

@pytest.mark.parametrize("input", [1, 2])
def test_parallel(resource, input):
    assert resource == "resource_data"
    assert input in [1, 2]

Execution Trace - 4 Steps

Step	Action	System State	Assertion	Result
1	Test runner starts and collects tests	Two test cases found: test_parallel with input=1 and input=2	-	PASS
2	Pytest initializes fixture 'resource' with scope='module'	Fixture setup prints 'Setup resource'	Fixture resource is created once for the module	PASS
3	Tests run in parallel threads/processes for input=1 and input=2	Both tests receive the same fixture instance 'resource_data'	Each test asserts resource == 'resource_data' and input in [1, 2]	PASS
4	After all tests complete, fixture teardown runs	Fixture teardown prints 'Teardown resource'	Fixture teardown happens once after all tests	PASS

Failure Scenario

Failing Condition: Fixture is not shared properly and recreated for each test in parallel causing inconsistent state

Execution Trace Quiz - 3 Questions

How many times is the fixture 'resource' set up when running these tests in parallel?

A Once per test parameter

B Once for the whole module

C Once per test function

D Once per test thread

Key Result

Using a fixture with module scope in pytest ensures the resource is created once and shared across parallel tests in the same module, improving efficiency and consistency.