pytest-best-practices
Expert guidance for writing high-quality pytest tests. Use when writing tests, setting up fixtures, parametrizing, mocking, or reviewing test code.
SKILL.md
Full skill instructions
<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_*.pyor*_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
assertstatements (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>
<routing>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>