Sync versus async tests

Choose the appropriate testing approach based on your test requirements. For standard API endpoint testing, use TestClient with regular functions. For tests requiring async operations (like database queries), use AsyncClient with proper async test configuration.

For synchronous tests:

from fastapi.testclient import TestClient
from app.main import app

client = TestClient(app)

def test_read_main():
    response = client.get("/")
    assert response.status_code == 200
    assert response.json() == {"message": "Hello World"}

For asynchronous tests:

import pytest
import httpx
from app.main import app

@pytest.mark.anyio
async def test_async_operations():
    async with httpx.AsyncClient(app=app, base_url="http://test") as client:
        response = await client.get("/")
        assert response.status_code == 200
        # Now you can use other async operations
        # await database.fetch_one("SELECT * FROM items")

Remember that async tests require additional setup:

1. Install the appropriate pytest plugin (pytest-anyio or pytest-asyncio)
2. Mark your test functions with the correct decorator
3. Use async def for the test function
4. Use AsyncClient instead of TestClient

This approach ensures your tests can properly interact with both your FastAPI application and any external asynchronous dependencies without blocking or creating concurrency issues.