pytest-best-practices

<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