Weird patching behavior

Question

I have one class (Cat) and one method (say_hello) to patch. When I patch the class only, everything works well. When I patch the method only, it works too. When I patch both at the same time, the class is not patched but the method is properly patched.

main.py

from hello import say_hello
from cat import Cat

cat = Cat('kitty')

def main():
    print(say_hello())

hello.py

def say_hello():
    return "No mocked"

test.py

import unittest
from unittest.mock import patch

class TestStringMethods(unittest.TestCase):
    # cat.Cat is not patched correctly if both patch statements are there
    @patch('cat.Cat')
    @patch('main.say_hello')
    def test_kitty(self, say_hello_mock, cat_mock):
        say_hello_mock.return_value = "Mocked"
        from main import main
        main()



if __name__ == '__main__':
    unittest.main()

If you run the previous example, a real Cat is created. If you comment the patch of main.say_hello, a mock Cat is created.

Answer 1

I don't know why the patch decorator is not working, but you can use this solution:

def test_kitty(self):
    with patch('cat.Cat') as cat_mock:
        with patch('main.say_hello') as hello_mock:
            from main import main
            main()