Python Testing Patterns

Python Testing Patterns Skill

Metadata (Tier 1)

Keywords: pytest, fixture, parametrize, mock, python test, unittest

File Patterns: test_*.py, *_test.py

Modes: testing_backend

Instructions (Tier 2)

Fixture Design

import pytest

@pytest.fixture
def database():
    """Create test database"""
    db = setup_database()
    yield db  # Provide to test
    teardown_database(db)  # Cleanup

def test_query(database):
    result = database.query("SELECT * FROM users")
    assert result is not None

Scopes: function (default), class, module, session

Parametrization

@pytest.mark.parametrize("input,expected", [
    (3, 9),
    (4, 16),
    (-2, 4),
])
def test_square(input, expected):
    assert square(input) == expected

Mocking

from unittest.mock import patch, MagicMock

def test_api_call():
    with patch('requests.get') as mock_get:
        mock_get.return_value.json.return_value = {'data': 'test'}

        result = fetch_data('https://api.example.com')

        assert result == {'data': 'test'}
        mock_get.assert_called_once()

Test Organization

tests/
├── unit/
│   ├── test_auth.py
│   └── test_models.py
├── integration/
│   └── test_api.py
└── conftest.py  # Shared fixtures

Anti-Patterns

❌ Test interdependence ❌ Mocking implementation details ❌ Not using fixtures for setup/teardown ❌ Hardcoded test data