How to mock a property inside a class in Python

Question

This is my first file called user.py

from account import Account    
class User:
   def __init__(self, id):
       self.id = id
       self._account = None

   @property
   def account(self):
       if not self._account:
          self._account = Account(self.id)

       return self._account

   @property
   def has_discount(self)
       return self.account.discount_id > 0

I have a second file called account.py

class Account:
    def __init__(self, user_id):
        # some process to load DB data
        self.account = load_account(user_id)
        # do something after this to initialize account properties like discount, etc

    @property
    def discount_id(self):
       return self.discount_id

My goal is to test user.py. One of the things I want to do is to mock the Account object in user.py for the 'has_discount' property decorator. I want to test different scenarios where has_discount will return either 0 or any other number.

How do I do this using patch where I can mock the Account object in the User class to return custom values so I can try different tests?

Answer 1

Because the user module imports Account in to its own namespace patching has to be done there instead of the account module. In other words you have to temporarily change what the name Account in the user module refers to:

from user import User
from unittest.mock import patch

with patch('user.Account') as MockAccount:
    MockAccount.return_value.discount_id = 1
    u = User(1)                             
    print(u.has_discount)
    # True

with patch('user.Account') as MockAccount:
    MockAccount.return_value.discount_id = 0
    u = User(1)
    print(u.has_discount)
    # False

I want to test different scenarios where has_discount will return either 0 or any other number.

In its current implementation User.has_discount will always return either True or False. Did you mean Account.discount_id?