def one_api(testCase, core):
    """
    Get the only API registered against a given MimicCore.

    :return: 2-tuple of ``region`` and ``service_id``
    """
    service_id = None
    api = None

    # Since there is only 1 API it can be assumed to be either an internal
    # or external API.
    if len(core._uuid_to_api_external):
        service_id, api = next(iter(core._uuid_to_api_external.items()))
    else:
        service_id, api = next(iter(core._uuid_to_api_internal.items()))
    region = api.catalog_entries(tenant_id=None)[0].endpoints[0].region
    return (region, service_id)