pytest

Basic Test Structure

import pytest

class TestUserService:
    def test_create_user_success(self):
        user = create_user(name="John", email="[email protected]")
        assert user.name == "John"
        assert user.email == "[email protected]"

    def test_create_user_invalid_email_fails(self):
        with pytest.raises(ValueError, match="Invalid email"):
            create_user(name="John", email="invalid")

Fixtures

import pytest

@pytest.fixture
def user():
    """Create a test user."""
    return User(name="Test User", email="[email protected]")

@pytest.fixture
def authenticated_client(client, user):
    """Client with authenticated user."""
    client.force_login(user)
    return client

# Fixture with teardown
@pytest.fixture
def temp_file():
    path = Path("/tmp/test_file.txt")
    path.write_text("test content")
    yield path  # Test runs here
    path.unlink()  # Cleanup after test

# Fixture scopes
@pytest.fixture(scope="module")  # Once per module
@pytest.fixture(scope="class")   # Once per class
@pytest.fixture(scope="session") # Once per test session

conftest.py

# tests/conftest.py - Shared fixtures
import pytest

@pytest.fixture
def db_session():
    session = create_session()
    yield session
    session.rollback()

@pytest.fixture
def api_client():
    return TestClient(app)

Mocking

from unittest.mock import patch, MagicMock

class TestPaymentService:
    def test_process_payment_success(self):
        with patch("services.payment.stripe_client") as mock_stripe:
            mock_stripe.charge.return_value = {"id": "ch_123", "status": "succeeded"}

            result = process_payment(amount=100)

            assert result["status"] == "succeeded"
            mock_stripe.charge.assert_called_once_with(amount=100)

    def test_process_payment_failure(self):
        with patch("services.payment.stripe_client") as mock_stripe:
            mock_stripe.charge.side_effect = PaymentError("Card declined")

            with pytest.raises(PaymentError):
                process_payment(amount=100)

# MagicMock for complex objects
def test_with_mock_object():
    mock_user = MagicMock()
    mock_user.id = "user-123"
    mock_user.name = "Test User"
    mock_user.is_active = True

    result = get_user_info(mock_user)
    assert result["name"] == "Test User"