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

pytest-advanced