<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>

Built-in fixtures — reach for these before writing your own; pytest already isolates and reverts them per test.

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
pytest -n auto               # Parallel across CPU cores (pytest-xdist)

</quick_reference>

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