pytest

pytest

Test behavior, not implementation. Tests are executable documentation — if the test name doesn't explain what the code does, rewrite it.

pytest is Python's standard testing framework. It uses plain assert statements, fixtures for setup/teardown, and a rich plugin ecosystem. All patterns target Python 3.14+.

References

• Fixture patterns, scope, factories, teardown — [${CLAUDE_SKILL_DIR}/references/fixtures.md]: Fixture lifecycle, yield fixtures, factory pattern, request object, parametrized fixtures
• Parametrize patterns, indirect, IDs — [${CLAUDE_SKILL_DIR}/references/parametrize.md]: Multi-parameter examples, indirect fixtures, custom IDs, stacking decorators
• Monkeypatch patterns, scoped patches — [${CLAUDE_SKILL_DIR}/references/monkeypatch.md]: API overview, attribute/env/dict patching, scoped monkeypatch, common recipes
• Plugin ecosystem and configuration — [${CLAUDE_SKILL_DIR}/references/plugins.md]: pytest-asyncio, pytest-mock, pytest-xdist, pytest-cov configuration patterns

Test Structure

Discovery and Naming

• Files: test_*.py or *_test.py. Prefer test_<module>.py matching source module.
• Functions: test_<behavior> — describe the behavior, not the method: test_returns_empty_list_when_no_matches not test_search.
• Classes: TestClassName groups related tests. No __init__ method. Use classes when tests share setup; use bare functions for independent tests.
• conftest.py is auto-discovered — no import needed. Place shared fixtures at the appropriate directory level.

Arrange-Act-Assert

Structure every test in three phases:

def test_user_creation_sets_defaults():
    # Arrange
    data = {"name": "Alice", "email": "[email protected]"}

    # Act
    user = User.from_dict(data)

    # Assert
    assert user.name == "Alice"
    assert user.is_active is True
    assert user.roles == []

• One act per test. If you need multiple acts, write multiple tests.
• Comments optional when phases are obvious. Add when the test is long enough that phases aren't immediately clear.