async def connection_handler(...):
    ...

async def test(stop_request):
    # occasionally stop the server
    while True:
        await asyncio.sleep(1)
        print('requesting stop')
        stop_request.set()

async def main():
    stop_request = asyncio.Event()
    asyncio.create_task(test(stop_request))
    while True:
        print('starting the server')
        server = await websockets.serve(connection_handler, 'localhost', 6789)
        await stop_request.wait()
        stop_request.clear()
        print('stopping the server')
        server.close()
        await server.wait_closed()

asyncio.run(main())