Fixture scope with parallel tests in PyTest - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding fixture scope behavior in parallel pytest runs

In pytest, when running tests in parallel using pytest-xdist, which fixture scope ensures that a fixture is created once per worker process?

A function

B session

C module

D package

💡 Hint

Think about the widest scope that pytest-xdist respects per worker.

The session scope creates the fixture once per worker process when running tests in parallel with pytest-xdist. Other scopes like module or function create fixtures more frequently.

❓ Predict Output

intermediate

Output of fixture usage with 'module' scope in parallel tests

Consider this pytest code run with 2 parallel workers using pytest-xdist:

import pytest

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

def test_one(resource):
    pass

def test_two(resource):
    pass

How many times will 'Setup resource' be printed?

A 0

B 1

C 4

D 2

💡 Hint

Remember that each worker runs tests independently and module scope is per module per worker.

With 2 workers, each runs the module's tests once, so the module-scoped fixture setup runs once per worker, totaling 2 times.

❓ assertion

advanced

Correct assertion for fixture usage count in parallel tests

You want to assert that a fixture with 'session' scope is created exactly once per worker when running 3 parallel pytest workers.

Which assertion correctly verifies this if setup_count tracks the number of fixture setups?

PyTest

def test_fixture_count(setup_count):
    # assert here
    pass

A assert setup_count == 3

B assert setup_count == 1

C assert setup_count >= 3

D assert setup_count <= 1

💡 Hint

Each worker runs its own session-scoped fixture instance.

With 3 workers, each creates its own session-scoped fixture, so the total setup count should be 3.

🔧 Debug

advanced

Debugging fixture sharing issue in parallel pytest

You have a fixture with 'session' scope but notice it runs multiple times when running tests in parallel with pytest-xdist. What is the most likely cause?

A The fixture scope is ignored when using pytest-xdist

B The fixture is defined inside a test function, causing multiple runs

C Each worker process has its own session, so fixture runs once per worker

D The fixture uses yield instead of return, causing multiple setups

💡 Hint

Think about how pytest-xdist manages processes.

pytest-xdist runs tests in separate worker processes, each with its own session. So session-scoped fixtures run once per worker, not globally.

❓ framework

expert

Best practice for sharing expensive fixture setup across parallel pytest workers

You have an expensive setup fixture that you want to share across all parallel pytest workers to avoid repeated setup. Which approach is best?

A Use a session-scoped fixture combined with a shared external resource like a database or file system lock

B Set fixture scope to 'function' and rely on pytest-xdist to optimize

C Use module-scoped fixtures and run tests sequentially

D Use pytest's cache to store fixture state between workers automatically

💡 Hint

Think about sharing state beyond process boundaries.

pytest fixtures run per worker process; to share expensive setup, use external shared resources or locks combined with session scope.