python-testing

# Python Testing Skill ## When to Activate Activate this skill when: - Writing Python unit tests - Creating test files or test directories - Setting up pytest configuration - Working with test fixtures or mocking - Running tests or checking coverage ## Quick Commands ```bash # Run all tests uv run pytest # Run specific file uv run pytest tests/test_auth.py # Run with coverage uv run pytest --cov=src --cov-report=html # Run verbose with output uv run pytest -v -s # Run tests matching pattern uv run pytest -k "test_user" # Run last failed uv run pytest --lf ``` ## Test Structure: AAA Pattern Follow **Arrange-Act-Assert** for clear, maintainable tests: ```python def test_user_registration(): # Arrange - set up test data email = "test@example.com" password = "secure_pass123" user_service = UserService() # Act - execute the function result = user_service.register(email, password) # Assert - verify the outcome assert result.success is True assert result.user.email == email ``` ## Directory Structure ``` project/ ├── src/ │ └── myapp/ ├── tests/ │ ├── conftest.py # Shared fixtures │ ├── unit/ │ │ └── test_utils.py │ ├── integration/ │ │ └── test_api.py │ └── e2e/ │ └── test_workflows.py └── pyproject.toml ``` ## Fixtures (conftest.py) ```python import pytest from myapp import create_app @pytest.fixture def app(): """Create application for testing.""" app = create_app("testing") yield app @pytest.fixture def client(app): """Create test client.""" return app.test_client() @pytest.fixture def sample_user(): """Create a sample user for testing.""" return User(email="test@example.com", username="testuser") ``` ## Parametrized Tests ```python @pytest.mark.parametrize("email,expected", [ ("valid@example.com", True), ("invalid.email", False), ("special+chars@test.co.uk", True), ]) def test_email_validation(email, expected): assert is_valid_email(email) == expected ``` ## Mocking ```python from unittest.mock import Mock, patch def test_api_call(): mock_response = Mock() mock_response.json.return_value = {"data": "success"} with patch("requests.get", return_value=mock_response): result = fetch_data("https://api.example.com") assert result == {"data": "success"} ``` ## Common Patterns ### Testing Exceptions ```python def test_division_by_zero(): with pytest.raises(ValueError, match="Cannot divide by zero"): divide(10, 0) ``` ### Testing with Temp Files ```python def test_file_processing(tmp_path): test_file = tmp_path / "test.txt" test_file.write_text("Hello World") result = process_file(str(test_file)) assert result.word_count == 2 ``` ### Testing Environment Variables ```python def test_config_from_env(monkeypatch): monkeypatch.setenv("API_KEY", "test_key_123") assert load_config().api_key == "test_key_123" ``` ## Coverage Configuration ```toml # pyproject.toml [tool.pytest.ini_options] testpaths = ["tests"] addopts = "-v --cov=src --cov-report=term-missing" [tool.coverage.run] source = ["src"] omit = ["tests/*"] ``` ## Naming Conventions - Test files: `test_*.py` - Test functions: `test_*` - Test classes: `Test*` ## Related Resources See `AgentUsage/testing_python.md` for complete documentation including: - Async testing patterns - Integration test examples - CI/CD integration - Test priority guidelines