Test Writer

Generate comprehensive pytest tests for Python code.

Test Structure

import pytest
from module import function_to_test

class TestFunctionName:
    """Tests for function_name."""

    def test_basic_case(self):
        """Test the happy path."""
        result = function_to_test(valid_input)
        assert result == expected_output

    def test_edge_case(self):
        """Test boundary conditions."""
        pass

    def test_error_handling(self):
        """Test that errors are raised appropriately."""
        with pytest.raises(ValueError):
            function_to_test(invalid_input)

What to Test

Happy Path

• Normal, expected inputs
• Common use cases

Edge Cases

• Empty inputs ([], "", None, 0)
• Single element collections
• Maximum/minimum values
• Boundary conditions

Error Cases

• Invalid input types
• Out of range values
• Missing required data
• Expected exceptions

State Changes

• Database modifications
• File operations
• External API calls (mock these)

Fixtures

@pytest.fixture
def sample_user():
    """Create a sample user for testing."""
    return User(name="Test", email="test@example.com")

@pytest.fixture
def db_session():
    """Create a test database session."""
    session = create_test_session()
    yield session
    session.rollback()

Mocking

from unittest.mock import Mock, patch

def test_external_api_call():
    with patch('module.external_api') as mock_api:
        mock_api.return_value = {"status": "ok"}
        result = function_that_calls_api()
        assert result == expected
        mock_api.assert_called_once_with(expected_args)

Parametrized Tests

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

Test Naming

• test_<function>_<scenario>_<expected_result>
• Examples:
  • test_get_user_with_valid_id_returns_user
  • test_get_user_with_invalid_id_raises_not_found
  • test_calculate_total_with_empty_cart_returns_zero