pytest-advanced

# 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

```toml
# 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",
]
```

```python
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](references/custom-plugins.md) for plugin development.

### Parallel Execution (pytest-xdist)

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

```python
@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](references/xdist-parallel.md) for distribution modes.

### Factory Fixtures

```python
@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