def get_longest_server_address(device):
    """
    get the longest server address from the devices's testbed
    Args:
        device ('obj'): Device object
    Returns:
        the longest address in the testbed
    """
    addresses = []
    for server in device.testbed.servers.values():
        addr = server.get('address', '')
        if isinstance(addr, list):
            addresses.extend(addr)
        else:
            addresses.append(addr)

    return max(addresses, key=len)