invalid format of client's host in testclient

[pjknkda]

According to ASGI specification, scope["client"] for HTTP and Websocket protocol should have its host value in either IPv4 or IPv6 address formats.

However, in starlette/testclient.py, the _TestClientTransport set its host value to "testclient" and breaks applications that expect IPv4 or IPv6 address formats during tests.

starlette/starlette/testclient.py

Line 246 in f7bf741

"client": ["testclient", 50000],

starlette/starlette/testclient.py

Line 264 in f7bf741

"client": ["testclient", 50000],

[bevinhex]

Same here, it is breaking my tests that expecting IP

[toxadx]

The specification of ASGI message format: https://asgi.readthedocs.io/en/latest/specs/www.html?highlight=scope%5B%22client%22%5D#http-connection-scope

client (Iterable[Unicode string, int]) – A two-item iterable of [host, port], where host is the remote host’s IPv4 or IPv6 address, and port is the remote port as an integer. Optional; if missing defaults to None.

[Kludex]

I've created #2295.