How to create a fake StringSession for unit tests - telethon

Question

I've got some code which uses StringSession to talk to the Telegram API using telethon.
In my unit tests, I'm trying to instantiate a mocked TelegramClient, passing it a StringSession(myvalue) object as the first parameter. The real code works fine, but I need a fake session string for 'myvalue', to use in my unit tests (where I have a mocked telegram client).
How can I create a dummy value for 'myvalue' which will successfully execute StringSession(myvalue)?
Currently, my tests are dying here:
self = <telethon.sessions.string.StringSession object at 0x7f0777492ad0>
string = 'dummyxxx'
def __init__(self, string: str = None):
super().__init__()
if string:
if string[0] != CURRENT_VERSION:
raise ValueError('Not a valid string')
string = string[1:]
ip_len = 4 if len(string) == 352 else 16
> self._dc_id, ip, self._port, key = struct.unpack(
_STRUCT_PREFORMAT.format(ip_len), StringSession.decode(string))
E struct.error: unpack requires a buffer of 275 bytes

Answer 1

If you don't need a valid session to start with, you can also use MemorySession instead:
from telethon.sessions import MemorySession
session = MemorySession()
# use session variable when creating the client

Answer 2

Someone posted an answer which helped point me in the right direction, but they later deleted it for some reason.
In case it helps anyone else, here is the code that worked for me:
import struct
import base64
from telethon.sessions import StringSession
_STRUCT_PREFORMAT = '>B{}sH256s'
CURRENT_VERSION = '1'
dc_id = 1
ip = b'\x7f\x00\x00\x01' # 127.0.0.1
port = 80
key = b'\x00' * 256
string = StringSession.encode(struct.pack(
_STRUCT_PREFORMAT.format(len(ip)),
dc_id,
ip,
port,
key
))
myvalue = CURRENT_VERSION + string
# Create the StringSession object using the dummy value to confirm it works
session = StringSession(myvalue)
print(myvalue)