Some pseude test code.

gistfile1.py

# my_app.py
from math import power

def some_fun(i):
  if power(i) > 10:
    return True
    
  return False

# test_my_app.py
from my_app import some_func
from math import power

def mock_power(i):
  # Real implemention of power is very, very complex. 
  # But I don't care how it works. When I insert some
  # value in my test I expect that it returns 5. And I
  # want to test how my software handles this response.
  return 5
   
power = mock_power

test_my_func():
  assert test_my_func(5) is False