pytest-type-safety

Pytest Type Safety

Quick Start

Add type annotations to every test function and fixture:

from __future__ import annotations

from typing import Any, AsyncGenerator
from unittest.mock import AsyncMock
import pytest

# ✅ Type annotations on fixture
@pytest.fixture
def create_test_order() -> Any:
    def _create(order_id: str = "123") -> Order:
        return Order(...)
    return _create

✅ Type annotations on test

@pytest.mark.asyncio async def test_extract_orders( create_test_order: Any, mock_gateway: AsyncMock, ) -> None: """Test function with full type safety.""" use_case = ExtractOrdersUseCase(gateway=mock_gateway) result = await use_case.execute() assert result is not None


## When to Use

- Write type-safe tests
- Configure mypy for test files
- Use protocols for mocks
- Enforce type checking in CI/CD
- Debug type-related test issues

## Key Patterns

### Test Functions

```python
def test_product_title() -> None:
    """Test product title creation."""
    title: ProductTitle = ProductTitle("Laptop")
    assert title.value == "Laptop"

Fixtures

@pytest.fixture
def create_test_line_item() -> Callable[..., LineItem]:
    """Factory for creating line items."""
    def _create(
        product_id: str = "prod_1",
        title: str = "Test Product",
        quantity: int = 1,
    ) -> LineItem:
        return LineItem(...)
    return _create

Create_Autospec for Type-Safe Mocks

from unittest.mock import create_autospec

# ✅ Mock with autospec enforces interface
def test_with_autospec() -> None:
    mock = create_autospec(ShopifyPort, instance=True)
    mock.fetch_orders.return_value = []
    # mock.typo_method() raises AttributeError

Mypy Configuration

# pyproject.toml
[tool.mypy]
python_version = "3.11"
strict = true
disallow_untyped_defs = true

[[tool.mypy.overrides]]
module = "tests.*"
disallow_untyped_defs = true
disallow_any_unimported = false  # Allow Any from fixtures

Type-Safe Assertions

def test_order_type_safe(create_test_order: Any) -> None:
    order: Order = create_test_order()
    
    assert isinstance(order, Order)
    assert isinstance(order.customer_name, str)

Supporting Files

File	Purpose
references/type-safety-patterns.md	Complete patterns and CI/CD integration

Requirements

Python 3.11+
pytest >= 7.0
mypy >= 1.7.0
pyright >= 1.1.0 (optional)

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