<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

code

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

bash

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>