This is not a nice solution:

def handler(request):
    resp = httpx.Response(200, json={"text": "Hello, world!"})
    resp.elapsed = timedelta(.......
    return resp

If you have dispatch code in that handler that can easily get boilerplatey.

I think httpx should do either of these:

• MockTransport take the duration as an optional argument
• httpx provide a decorator, so you can wrap your handler in it
• automatically set a duration of 0 for manually created Response objects - why error out if the data is already there?