# test_example.py
def add(a, b):
    return a + b

def test_add():
    """Basic test example."""
    result = add(2, 3)
    assert result == 5

def test_add_negative():
    """Test with negative numbers."""
    assert add(-1, 1) == 0

# Run with: uv run pytest test_example.py

# test_calculator.py
import pytest

class Calculator:
    """Simple calculator for testing."""

    def add(self, a: float, b: float) -> float:
        return a + b

    def divide(self, a: float, b: float) -> float:
        if b == 0:
            raise ValueError("Cannot divide by zero")
        return a / b


def test_addition():
    """Test addition."""
    calc = Calculator()
    assert calc.add(2, 3) == 5
    assert calc.add(-1, 1) == 0


def test_division_by_zero():
    """Test division by zero raises error."""
    calc = Calculator()
    with pytest.raises(ValueError, match="Cannot divide by zero"):
        calc.divide(5, 0)

# test_database.py
import pytest

@pytest.fixture
def db():
    """Fixture that provides connected database."""
    # Setup
    database = {"connected": True}
    yield database
    # Teardown
    database["connected"] = False


def test_database_query(db):
    """Test using fixture."""
    assert db["connected"] is True

# test_validation.py
import pytest

@pytest.mark.parametrize("email,expected", [
    ("user@example.com", True),
    ("invalid.email", False),
])
def test_email_validation(email, expected):
    """Test email validation with various inputs."""
    assert is_valid(email) == expected

# test_api_client.py
import pytest
from unittest.mock import Mock, patch

def test_api_call():
    """Test API call with mock."""
    mock_response = Mock()
    mock_response.json.return_value = {"id": 1}

    with patch("requests.get", return_value=mock_response):
        result = get_user(1)
        assert result["id"] == 1

# test_exceptions.py
import pytest

def test_exception():
    """Test exception is raised."""
    with pytest.raises(ValueError, match="error message"):
        divide(10, 0)

# tests/
#   __init__.py
#   conftest.py           # Shared fixtures
#   test_unit/            # Unit tests
#   test_integration/     # Integration tests
#   test_e2e/            # End-to-end tests

# Good test names describe what is tested and expected outcome
def test_user_creation_with_valid_data():
    pass

def test_login_fails_with_invalid_password():
    pass

# Bad test names
def test_1():  # Not descriptive
    pass

def test_user():  # Too vague
    pass

import pytest

@pytest.mark.slow
def test_slow_operation():
    pass

@pytest.mark.integration
def test_database_integration():
    pass

# Run with:
# uv run pytest -m slow          # Run only slow tests
# uv run pytest -m "not slow"    # Skip slow tests