setup-backend-testing

name	setup-backend-testing
description	Scaffolds the testing infrastructure for a FastAPI (Pydantic V2) backend using Pytest. Configures Dockerized DB, directory structure, and modern pyproject.toml settings.

Setup Backend Testing

Procedure

1. Analyze Context

1. Locate app/main.py, pyproject.toml, and requirements.txt.
2. Confirm Pydantic V2 is installed (pydantic>=2.0).

2. Install Dev Dependencies

Add the following to requirements-dev or poetry group:

• pytest, pytest-cov
• pytest-mock (Wrapper around unittest.mock)
• pytest-asyncio (Critical for async Pydantic/FastAPI tests) [10]
• httpx (For API integration tests)
• polyfactory (Recommended for Pydantic V2) OR factory-boy
• respx (For mocking external HTTP services) [5]

3. Scaffold Directory Structure

Create the hierarchy ensuring separation of concerns [11]:

backend/tests/
├── unit/
├── integration/
├── contract/
├── factories/        # Pydantic Model Factories
├── conftest.py       # Global fixtures (DB session, AsyncClient)
└── pyproject.toml    # Configuration (instead of pytest.ini)

4. Configure conftest.py

Generate fixtures for: • Async Client: httpx.AsyncClient with base_url="http://test". • DB Session: A session strictly bound to the test transaction (rollback strategy). • Schema Lifecycle: A scope="session" fixture that creates the DB schema (e.g., Base.metadata.create_all(bind=engine)) at start and drops it at finish. This guarantees tests work even if test.db doesn't exist. • Event Loop: Override default event loop scope to session if using async fixtures.

5. Configure pyproject.toml

Inject the following configuration to handle Asyncio and warnings properly:

[tool.pytest.ini_options]
minversion = "6.0"
addopts = "-v --strict-markers --cov=app --cov-report=term-missing"
asyncio_mode = "auto"
testpaths = ["tests"]
markers = [
    "unit: Fast tests, no I/O [12]",
    "integration: Requires Docker/DB [12]",
    "contract: OpenAPI schema validation [12]",
]
filterwarnings = [
    "ignore::DeprecationWarning", # Filter noise from third-party libs
]

6. Create Baseline Tests (Pydantic V2 Style)

• tests/unit/test_smoke.py: Verify a Pydantic model uses model_validate correctly. • tests/integration/test_health.py: Full async HTTP request to health endpoint.

Constraints

• DO NOT use pytest.ini if pyproject.toml exists; consolidate config. • ENSURE asyncio_mode = "auto" is set to avoid decorators on every async test.