Pytest Production Test Suite Guidelines

Standards & Best Practices

1. Directory Structure: Mirror src/ inside tests/ (e.g. src/services/billing.py ➔ tests/services/test_billing.py).
2. Fixtures over Shared State: Use explicit @pytest.fixture with appropriate scopes (function, session).
3. Async Testing: Use pytest-asyncio with @pytest.mark.asyncio.

Reference Test Suite with Mocking & Parametrization

import pytest
from unittest.mock import AsyncMock
from src.services.tax_calculator import calculate_tax

@pytest.fixture
def mock_currency_service():
    service = AsyncMock()
    service.get_exchange_rate.return_value = 1.25
    return service

@pytest.mark.parametrize("subtotal,rate,expected_tax", [
    (100.0, 0.20, 20.0),
    (50.0, 0.10, 5.0),
    (0.0, 0.20, 0.0),
])
def test_calculate_tax_parametrized(subtotal, rate, expected_tax):
    tax = calculate_tax(subtotal=subtotal, tax_rate=rate)
    assert tax == pytest.approx(expected_tax, 0.01)

@pytest.mark.asyncio
async def test_currency_conversion_async(mock_currency_service):
    rate = await mock_currency_service.get_exchange_rate("GBP", "USD")
    assert rate == 1.25
    mock_currency_service.get_exchange_rate.assert_awaited_once_with("GBP", "USD")

Running Tests with Coverage

pytest --cov=src --cov-report=term-missing --cov-fail-under=85