pytest-best-practices Skill

<objective> Provide pytest best practices and patterns for writing maintainable, efficient tests. </objective>

<essential_principles>

Test Independence

Each test must run in isolation - no shared state between tests
Use fixtures for setup/teardown, never class-level mutable state
Tests should pass regardless of execution order

Naming Conventions

Files: test_*.py or *_test.py
Functions: test_<description>()
Classes: Test<ClassName>
Fixtures: descriptive lowercase_with_underscores

Directory Structure

tests/
├── conftest.py          # Shared fixtures
├── unit/
│   └── test_module.py
├── integration/
│   └── test_api.py
└── fixtures/            # Test data files

Core Testing Rules

Use plain assert statements (pytest provides detailed failure messages)
One logical assertion per test when practical
Test edge cases: empty inputs, boundaries, invalid data, errors
Keep tests focused and readable

</essential_principles>

<quick_reference>

| Pattern | Use Case | |---------|----------| | @pytest.fixture | Setup/teardown, dependency injection | | @pytest.mark.parametrize | Run test with multiple inputs | | @pytest.mark.skip | Skip test temporarily | | @pytest.mark.xfail | Expected failure (known bug) | | pytest.raises(Exception) | Test exception raising | | pytest.approx(value) | Float comparison | | mocker.patch() | Mock dependencies | | conftest.py | Share fixtures across modules |

Common Commands

pytest -v                    # Verbose
pytest -x                    # Stop on first failure
pytest --lf                  # Run last failed
pytest -k "pattern"          # Match test names
pytest -m "marker"           # Run marked tests
pytest --cov=src             # Coverage report

</quick_reference>

Based on what you're doing, read the relevant reference:

| Task | Reference | |------|-----------| | Setting up fixtures, scopes, factories | references/fixtures.md | | Parametrizing tests, multiple inputs | references/parametrization.md | | Mocking, patching, faking dependencies | references/mocking.md | | Markers, exceptions, assertions, async | references/patterns.md |

</routing> <dependencies> ```bash pip install pytest pytest-asyncio pytest-mock pytest-cov pytest-xdist ``` </dependencies>

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