AsyncClient and testing StreamingResponse in FastAPI

[denjas]

client = httpx.AsyncClient(app=app)
async with client.stream('GET', 'https://www.example.com/') as response:
    async for chunk in response.aiter_bytes():
        process(chunk)

This code works fine and receives data in chunked if the app parameter for AsyncClient is not specified but waits for all parts and only after that gives the data if you specify the app parameter. Please help me figure out what the problem is. In FastAPI I use the default settings for StreamingResponse and pass an asynchronous generator to it.

fastapi==0.94.1
httpx==0.23.3
python 3.11

I am using httx for api testing via pytest and pytest-asyncio