Test is subclassing BaseHTTPMiddleware

The current middleware subclasses BaseHTTPMiddleware which per encode/starlette#919 and tiangolo/fastapi#2086 will cause all background tasks to run before the response is sent.

Start by inspecting the middleware that subclasses BaseHTTPMiddleware and read encode/starlette#919 and tiangolo/fastapi#2086 for the reported response and background-task behavior. Done means the middleware no longer causes background tasks to run before the response is sent, with the relevant behavior verified.

索引モデルが issue の本文から書いたものです。