Advanced Pytest Patterns

Advanced pytest features for robust, maintainable test suites.

When to Use This Skill

Use this skill when... Use python-testing instead when...

Writing fixtures with scopes/factories Basic test structure questions

Parametrizing with complex data Simple assert patterns

Setting up pytest plugins (cov, xdist) Running existing tests

Organizing conftest.py hierarchy Test discovery basics

Async testing with pytest-asyncio Synchronous unit tests

Installation

Core + common plugins

uv add --dev pytest pytest-cov pytest-asyncio pytest-xdist pytest-mock

Configuration (pyproject.toml)

[tool.pytest.ini_options] testpaths = ["tests"] addopts = [ "-v", "--strict-markers", "--tb=short", "-ra", "--cov=src", "--cov-report=term-missing", "--cov-fail-under=80", ] markers = [ "slow: marks tests as slow (deselect with '-m "not slow"')", "integration: marks tests as integration tests", ] asyncio_mode = "auto"

[tool.coverage.run] branch = true source = ["src"]

[tool.coverage.report] exclude_lines = ["pragma: no cover", "if TYPE_CHECKING:", "@abstractmethod"]

Fixtures

Scopes and Lifecycle

import pytest from typing import Generator

function (default) - fresh per test

@pytest.fixture def db() -> Generator[Database, None, None]: database = Database(":memory:") database.create_tables() yield database database.close()

session - shared across all tests

@pytest.fixture(scope="session") def app(): return create_app("testing")

autouse - applies automatically

@pytest.fixture(autouse=True) def reset_state(): clear_cache() yield

Scope Lifetime

function

Each test (default)

class

Each test class

module

Each test file

session

Entire test run

Parametrized Fixtures

@pytest.fixture(params=["sqlite", "postgres", "mysql"]) def database_backend(request) -> str: return request.param # Test runs 3 times

Indirect parametrization

@pytest.fixture def user(request) -> User: return User(**request.param)

@pytest.mark.parametrize("user", [ {"name": "Alice", "age": 30}, {"name": "Bob", "age": 25}, ], indirect=True) def test_user_validation(user: User): assert user.name

Factory Pattern

@pytest.fixture def user_factory() -> Callable[[str], User]: created: list[User] = [] def _create(name: str, **kwargs) -> User: user = User(name=name, **kwargs) created.append(user) return user yield _create for u in created: u.delete()

Markers

Built-in markers

@pytest.mark.skip(reason="Not implemented") @pytest.mark.skipif(sys.version_info < (3, 12), reason="Requires 3.12+") @pytest.mark.xfail(reason="Known bug #123") @pytest.mark.timeout(10)

Parametrize

@pytest.mark.parametrize("input,expected", [ pytest.param(2, 4, id="two"), pytest.param(3, 9, id="three"), pytest.param(-2, 4, id="negative"), ]) def test_square(input: int, expected: int): assert input ** 2 == expected

Run by marker

pytest -m unit # Only unit tests pytest -m "not slow" # Skip slow tests pytest -m "integration and not slow" # Combine markers

Key Plugins

Plugin Purpose Key Command

pytest-cov Coverage pytest --cov=src --cov-report=term-missing

pytest-xdist Parallel pytest -n auto

pytest-asyncio Async tests asyncio_mode = "auto" in config

pytest-mock Mocking mocker fixture

pytest-timeout Timeouts @pytest.mark.timeout(10)

Async Testing (pytest-asyncio)

@pytest.mark.asyncio async def test_async_function(): result = await fetch_data() assert result is not None

@pytest.fixture async def async_client() -> AsyncGenerator[AsyncClient, None]: async with AsyncClient() as client: yield client

Mocking (pytest-mock)

def test_with_mock(mocker): mock_api = mocker.patch("myapp.external.api_call") mock_api.return_value = {"data": "test"} result = my_function() assert result["data"] == "test" mock_api.assert_called_once()

Running Tests

Execution

pytest # All tests pytest tests/test_models.py::test_user # Specific test pytest -k "user and not slow" # Pattern matching

Parallel

pytest -n auto # All CPUs pytest -n 4 # 4 workers

Coverage

pytest --cov=src --cov-report=html --cov-report=term-missing

Failed tests

pytest --lf # Last failed only pytest --ff # Failed first pytest -x # Stop on first failure pytest --maxfail=3 # Stop after 3

Debugging

pytest -x --pdb # Debug on failure pytest -s # Show print output pytest --collect-only # Dry run

CI Integration

.github/workflows/test.yml

• name: Run tests run: | uv run pytest
  --cov=src
  --cov-report=xml
  --cov-report=term-missing
  --junitxml=test-results.xml

Agentic Optimizations

Context Command

Quick check pytest -x --tb=short -q

Fail fast pytest -x --maxfail=1 --tb=short

Parallel fast pytest -n auto -x --tb=short -q

Specific test pytest tests/test_foo.py::test_bar -v

By marker pytest -m "not slow" -x --tb=short

Coverage check pytest --cov=src --cov-fail-under=80 -q

CI mode pytest --junitxml=results.xml --cov-report=xml -q

Last failed pytest --lf --tb=short

Debug pytest -x --pdb -s

For detailed patterns on conftest.py hierarchy, async testing, test organization, and common patterns, see REFERENCE.md.