Pytest Patterns

Pytest Testing Patterns

When to Use This Skill

• Writing Python tests with pytest
• Creating test fixtures
• Mocking external dependencies
• Parametrized testing
• Testing best practices

Target Agents

• backend-developer - Testing Python code
• django-expert - Django testing
• qa-engineer - Test automation

Core Patterns

1. Basic Test Structure

import pytest

def test_addition():
    assert 1 + 1 == 2

def test_subtraction():
    assert 5 - 3 == 2

class TestMath:
    def test_multiply(self):
        assert 2 * 3 == 6

    def test_divide(self):
        assert 10 / 2 == 5

2. Fixtures

import pytest
from myapp import create_app, db

@pytest.fixture
def app():
    app = create_app('testing')
    with app.app_context():
        db.create_all()
        yield app
        db.drop_all()

@pytest.fixture
def client(app):
    return app.test_client()

@pytest.fixture
def user(app):
    user = User(email='test@example.com')
    db.session.add(user)
    db.session.commit()
    return user

def test_user_creation(user):
    assert user.email == 'test@example.com'

3. Parametrization

@pytest.mark.parametrize("input,expected", [
    (1, 2),
    (2, 4),
    (3, 6),
])
def test_double(input, expected):
    assert input * 2 == expected

@pytest.mark.parametrize("email,valid", [
    ("test@example.com", True),
    ("invalid-email", False),
    ("", False),
])
def test_email_validation(email, valid):
    assert validate_email(email) == valid

4. Mocking

from unittest.mock import Mock, patch

def test_api_call():
    with patch('requests.get') as mock_get:
        mock_get.return_value.json.return_value = {'data': 'test'}
        mock_get.return_value.status_code = 200

        result = fetch_data()

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

Best Practices

1. Use fixtures for setup
2. Parametrize similar tests
3. Mock external dependencies
4. Use pytest marks for categorization
5. Implement conftest.py for shared fixtures
6. Use pytest-cov for coverage
7. Write descriptive test names
8. Test edge cases
9. Keep tests independent
10. Use pytest-django for Django