[ Python 常見問題 ] Using mock patch to mock an instance method

Source From Here 
Question 
I'm trying to mock something while testing a Django app using the imaginatively named Mock testing library. I can't seem to quite get it to work, I'm trying to do this: 
- models.py 

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1. #!/usr/bin/env python3  
2. class Promotion(object):  
3.     def __init__(self):  
4.         pass  
5.   
6.     def bar(self):  
7.         return "Do something I don't want!"  

How do I mock the method bar of the creating object of class Promotion? 

How-To 
Check below sample code: 
- test.py 

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1. import models  
2. from unittest import TestCase  
3. from unittest.mock import patch  
4.   
5. class ViewsDoSomething(TestCase):  
6.     def setUp(self):  
7.         self.mockMsg = 'Do what I want'  
8.   
9.   
10.     @patch.object(models.Promotion, 'bar')  
11.     def test_enter_promotion(self, mockObj):  
12.         mockObj.return_value = self.mockMsg  
13.   
14.         p = models.Promotion()  
15.         self.assertTrue(p.bar() == self.mockMsg)  

Then you can test it this way: 

# pytest -v test.py
...
test.py::ViewsDoSomething::test_enter_promotion PASSED
...

Supplement 
* Python 文章收集 - 用 Mock 來做 Python Unit Test 
* Python 文章收集 - pytest introduction