starlette TestClient session was disappeared.

When you use https_only flag, you should set base_url as "https://testserver".

app = SessionMiddleware(
    app,
    secret_key="abracadabra",
    same_site="None",
    https_only=True  # When you use https_only flag,
)

from starlette.testclient import TestClient
TestClient(app, base_url="https://testserver")  # you should set base_url as "https://testserver".