[ Python 常見問題 ] Python Mocking a function from an imported module

Source From Here 
Question 
I want to understand how to @patch a function from an imported module. This is where I am so far. 
- app/mocking.py 

view plaincopy to clipboardprint?

1. from app.my_module import get_user_name  
2.   
3. def test_method():  
4.     return get_user_name()  
5.   
6. if __name__ == "__main__":  
7.     print("Starting Program...")  
8.     test_method()  

- app/my_module/__init__.py 

view plaincopy to clipboardprint?

1. def get_user_name():  
2.     return "Unmocked User"  

- test/mock_test.py 

view plaincopy to clipboardprint?

1. import unittest  
2. from unittest.mock import patch  
3. from app.mocking import test_method  
4.   
5.   
6. class MockingTestTestCase(unittest.TestCase):  
7.   
8.     @patch('app.my_module.get_user_name')  
9.     def test_mock_stubs(self, mock_method):  
10.         mock_method.return_value = 'Mocked This Silly'  
11.         ret = test_method()  
12.         self.assertEqual(ret, 'Mocked This Silly')  

Execution output: 

# pytest test/mock_test.py
...
@patch('app.my_module.get_user_name')
def test_mock_stubs(self, mock_method):
mock_method.return_value = 'Mocked This Silly'
ret = test_method()
> self.assertEqual(ret, 'Mocked This Silly')
E AssertionError: 'Unmocked User' != 'Mocked This Silly'
E - Unmocked User
E + Mocked This Silly

How-To 
When you are using the patch decorator from the unittest.mock package you are not patching the namespace the module is imported from (in this case app.my_module.get_user_name) you are patching it in the namespace under test app.mocking.get_user_name. To do the above with Mock try something like the below: 

view plaincopy to clipboardprint?

1. import unittest  
2. from unittest.mock import patch  
3. from app.mocking import test_method  
4.   
5.   
6. class MockingTestTestCase(unittest.TestCase):  
7.   
8.     @patch('app.mocking.get_user_name')  
9.     def test_mock_stubs(self, mock_method):  
10.         mock_method.return_value = 'Mocked This Silly'  
11.         ret = test_method()  
12.         self.assertEqual(ret, 'Mocked This Silly')  

Changing patch target from ''app.my_module.get_user_name'' to 'app.mocking.get_user_name'. The standard library documentation includes a useful section describing this.