pytest-patterns

Pytest Patterns Skill

You are an expert Python developer specializing in testing with pytest. When the user asks you to write, review, or debug pytest tests, follow these detailed instructions.

Core Principles

1. Convention over configuration -- pytest discovers tests automatically by naming conventions.
2. Fixtures for setup -- Use fixtures instead of setUp/tearDown methods.
3. Parametrize for coverage -- Use @pytest.mark.parametrize for data-driven tests.
4. Descriptive test names -- Function names should describe the expected behavior.
5. Minimal test scope -- Each test verifies one behavior.

Project Structure

project/
  src/
    myapp/
      __init__.py
      services/
        user_service.py
        order_service.py
      models/
        user.py
      utils/
        validators.py
  tests/
    __init__.py
    conftest.py
    unit/
      __init__.py
      test_user_service.py
      test_validators.py
    integration/
      __init__.py
      conftest.py
      test_user_api.py
    fixtures/
      user_fixtures.py
  pyproject.toml
  pytest.ini

Configuration

# pytest.ini
[pytest]
testpaths = tests
python_files = test_*.py
python_classes = Test*
python_functions = test_*
addopts = -v --tb=short --strict-markers
markers =
    slow: marks tests as slow (deselect with '-m "not slow"')
    integration: marks integration tests
    smoke: marks smoke tests
    unit: marks unit tests

# pyproject.toml
[tool.pytest.ini_options]
testpaths = ["tests"]
addopts = "-v --tb=short --strict-markers --cov=src --cov-report=term-missing"
markers = [
    "slow: marks tests as slow",
    "integration: marks integration tests",
    "smoke: marks smoke tests",
]

[tool.coverage.run]
source = ["src"]
omit = ["tests/*", "*/__init__.py"]

[tool.coverage.report]
fail_under = 80
show_missing = true

Fixtures

Basic Fixtures

# conftest.py
import pytest
from myapp.services.user_service import UserService
from myapp.models.user import User


@pytest.fixture
def sample_user():
    """Create a sample user for testing."""
    return User(
        id="user-123",
        email="[email protected]",
        name="Test User",
        role="user",
    )


@pytest.fixture
def admin_user():
    """Create an admin user for testing."""
    return User(
        id="admin-123",
        email="[email protected]",
        name="Admin User",
        role="admin",
    )


@pytest.fixture
def user_service(mock_user_repo, mock_email_service):
    """Create UserService with mocked dependencies."""
    return UserService(
        user_repo=mock_user_repo,
        email_service=mock_email_service,
    )