Basic Test Structure

import pytest

class TestUserService: def test_create_user_success(self): user = create_user(name="John", email="john@test.com") assert user.name == "John" assert user.email == "john@test.com"

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="test@example.com")

@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"

Parametrize

@pytest.mark.parametrize("input,expected", [ ("hello", "HELLO"), ("world", "WORLD"), ("pytest", "PYTEST"), ]) def test_uppercase(input, expected): assert input.upper() == expected

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

Markers

pytest.ini or pyproject.toml

[tool.pytest.ini_options] markers = [ "slow: marks tests as slow", "integration: marks integration tests", ]

Usage

@pytest.mark.slow def test_large_data_processing(): ...

@pytest.mark.integration def test_database_connection(): ...

@pytest.mark.skip(reason="Not implemented yet") def test_future_feature(): ...

@pytest.mark.skipif(sys.platform == "win32", reason="Unix only") def test_unix_specific(): ...

Run specific markers

pytest -m "not slow"

pytest -m "integration"

Async Tests

import pytest

@pytest.mark.asyncio async def test_async_function(): result = await async_fetch_data() assert result is not None

Commands

pytest # Run all tests pytest -v # Verbose output pytest -x # Stop on first failure pytest -k "test_user" # Filter by name pytest -m "not slow" # Filter by marker pytest --cov=src # With coverage pytest -n auto # Parallel (pytest-xdist) pytest --tb=short # Short traceback

Keywords

pytest, python, testing, fixtures, mocking, parametrize, markers