def METHOD_NAME(self):
    cid = CaseInsensitiveDict(
        {
            "Accept": "application/json",
            "user-Agent": "requests",
        }
    )
    keyset = frozenset(["Accept", "user-Agent"])
    assert frozenset(i[0] for i in cid.items()) == keyset
    assert frozenset(cid.keys()) == keyset
    assert frozenset(cid) == keyset