def METHOD_NAME(self):
    cid = CaseInsensitiveDict(
        {
            "Accept": "application/json",
            "user-Agent": "requests",
        }
    )
    keyset = frozenset(lowerkey for lowerkey, v in cid.lower_items())
    lowerkeyset = frozenset(["accept", "user-agent"])
    assert keyset == lowerkeyset