Advanced Pytest Patterns

Master pytest's advanced features for scalable, maintainable test suites.

Overview

• Building custom test markers for categorization

• Writing pytest plugins and hooks

• Configuring parallel test execution with pytest-xdist

• Creating reusable fixture patterns

• Optimizing test collection and execution

Quick Reference

Custom Markers

pyproject.toml

[tool.pytest.ini_options] markers = [ "slow: marks tests as slow (deselect with '-m "not slow"')", "integration: marks tests requiring external services", "smoke: critical path tests for CI/CD", ]

import pytest

@pytest.mark.slow def test_complex_analysis(): result = perform_complex_analysis(large_dataset) assert result.is_valid

Run: pytest -m "not slow" # Skip slow tests

Run: pytest -m smoke # Only smoke tests

See custom-plugins.md for plugin development.

Parallel Execution (pytest-xdist)

[tool.pytest.ini_options] addopts = ["-n", "auto", "--dist", "loadscope"]

@pytest.fixture(scope="session") def db_engine(worker_id): """Isolate database per worker.""" db_name = "test_db" if worker_id == "master" else f"test_db_{worker_id}" engine = create_engine(f"postgresql://localhost/{db_name}") yield engine

See xdist-parallel.md for distribution modes.

Factory Fixtures

@pytest.fixture def user_factory(db_session) -> Callable[..., User]: """Factory fixture for creating users.""" created = []

def _create(**kwargs) -> User:
    user = User(**{"email": f"u{len(created)}@test.com", **kwargs})
    db_session.add(user)
    created.append(user)
    return user

yield _create
for u in created:
    db_session.delete(u)

Key Decisions

Decision Recommendation

Parallel execution pytest-xdist with --dist loadscope

Marker strategy Category (smoke, integration) + Resource (db, llm)

Fixture scope Function default, session for expensive setup

Plugin location conftest.py for project, package for reuse

Async testing pytest-asyncio with auto mode

Anti-Patterns (FORBIDDEN)

NEVER use expensive fixtures without session scope

@pytest.fixture # WRONG - loads every test def model(): return load_ml_model() # 5s each time!

NEVER mutate global state

@pytest.fixture def counter(): global _counter _counter += 1 # WRONG - leaks between tests

NEVER skip cleanup

@pytest.fixture def temp_db(): db = create_db() yield db # WRONG - missing db.drop()!

NEVER use time.sleep (use mocking)

def test_timeout(): time.sleep(5) # WRONG - slows tests

Related Skills

• unit-testing

• Basic pytest patterns and AAA structure

• integration-testing

• Database and API testing patterns

• property-based-testing

• Hypothesis integration with pytest

References

• Xdist Parallel - Parallel execution patterns

• Custom Plugins - Plugin and hook development

• Conftest Template - Production conftest.py

Capability Details

custom-markers

Keywords: pytest markers, test categorization, smoke tests, slow tests Solves: Categorize tests, run subsets in CI, skip expensive tests

pytest-xdist

Keywords: parallel, xdist, distributed, workers, loadscope Solves: Run tests in parallel, worker isolation, optimize distribution

pytest-hooks

Keywords: hook, plugin, conftest, pytest_configure, collection Solves: Customize pytest behavior, add timing reports, reorder tests

fixture-patterns

Keywords: fixture, factory, async fixture, cleanup, scope Solves: Factory fixtures, async fixtures, ensure cleanup runs

parametrize-advanced

Keywords: parametrize, indirect, cartesian, pytest.param, xfail Solves: Test multiple scenarios, fixtures with params, expected failures