TestClient does not clear cookies based on response except if domain is set to testserver.local

[mlbiche]

Testing a response that delete a cookie with TestClient does not work except if domain is set to testserver.local.

This due to how cookiejar deletes cookies. If no domain is provided when deleting the cookie, the domain used to delete the cookie is set to request domain, being testserver.local (see cookiejar.py#L1532 + cookiejar.py#L645). If testserver domain is provided, the domain used to delete the cookie is set to testserver.local because it is required to be dotted. However, setting the cookie without domain or with testserver domain (being TestClient.base_url.host returned value), the cookie is stored in the cookie jar with the provided domain and not testserver.local.

I have written test cases to illustrate this situation : mlbiche@4adcaf0
I would expect all 3 test cases to succeed while only testserver.local does.

Also, note that this issue is even less expected with following code:

async def app(scope: Scope, receive: Receive, send: Send) -> None:
    response = Response("Hello, world!", media_type="text/plain")
    response.delete_cookie("mycookie")
    await response(scope, receive, send)

client = TestClient(app, cookies={ mycookie: "myvalue" })
client.get("/")
assert not len(client.cookies)  # This fails

As no domain is provided neither when initializing TestClient, neither when deleting the cookie, this would be expected to work. This fails because the cookie is set the cookie jar with empty domain while deleting always try to delete with testserver.local.

I have to admit that cookiejar behaviour is confusing for me : why would it always define a dotted domain when extracting cookies while the Cookie constructor let you define cookies without dotted domain (see cookiejar.py#L786.

However, as it does work this way, I starlette.TestClient or httpx2.Client should be updated and always set the domain :

• to Client.base_url.host + ".local" if no domain is provided in Cookies.set _models.py#L1104
• to domain + ".local" if the domain isn't dotted in Cookies.set

[mlbiche]

As the issue seems strongly related to httpx2, I have created another discussion on their side : pydantic/httpx2#1059