Server that returns whatever you ask it to

server.py

import wsgiref
import threading

@asynccontextmanager
async def http_server(headers: dict, body: bytes):
    def app(_, start_response):
        start_response("200 OK", list(headers.items()))
        return [body] if body else []

    server = wsgiref.simple_server.make_server("localhost", 0, app)
    threading.Thread(target=server.serve_forever).start()
    # Wait for the server to start
    await asyncio.sleep(0.1)

    try:
        yield f"http://localhost:{server.server_port}"
    finally:
        server.shutdown()