Using Mock with python

[Hocinema]

app_client.py
-------------
class AppClient:
       
    def __init__(self):
        self.val = "true"
    
    def get_value(self, feature_eng):
        return self.val
....................................................

app_client_instance.py
----------------------
from app_client import AppClient

app_client_instance = AppClient()
....................................................

feat_eng.py
-----------
from app_client_instance import app_client_instance

class FeatEng:

    @staticmethod
    def is_activ(feature_eng):
        client = app_client_instance
        value = client.get_value(feature_eng)
        return "true" == value
    
....................................................
test.py
-------


import unittest
from unittest.mock import MagicMock
from app_client import AppClient
from app_client_instance import app_client_instance
from feat_eng import FeatEng

class FeatEngShould(unittest.TestCase):

    def test_mockmagshouldFalse(self):
        client = MagicMock(spec=AppClient, name=AppClient)
        client.get_value.return_value = "false"
        instance = MagicMock()
        instance.app_client_instance.return_value = client
        result = FeatEng.is_activ("MIG_ENG")
        self.assertFalse(result) 

Error:

Output:
$ pytest test.py 
================================================================================== test session starts ===================================================================================
platform darwin -- Python 3.8.2, pytest-6.2.1, py-1.10.0, pluggy-0.13.1
rootdir: /Users/hocinema/projets/scripts/python
plugins: hypothesis-5.43.3, anyio-2.0.2
collected 1 item                                                                                                                                                                         

test.py F                                                                                                                                                                          [100%]

======================================================================================== FAILURES ========================================================================================
_______________________________________________________________________________ FeatEngShould.test_mockmag _______________________________________________________________________________

self = <test.FeatEngShould testMethod=test_mockmag>

    def test_mockmag(self):
        client = MagicMock(spec=AppClient, name=AppClient)
        client.get_value.return_value = "false"
        instance = MagicMock()
        instance.app_client_instance.return_value = client
        result = FeatEng.is_activ("MIG_ENG")
>       self.assertFalse(result)
E       AssertionError: True is not false

test.py:16: AssertionError
================================================================================ short test summary info =================================================================================
FAILED test.py::FeatEngShould::test_mockmag - AssertionError: True is not false
=================================================================================== 1 failed in 0.21s ====================================================================================

I want to make the mock client returning false to make success the test but instead it failed