Patching: Replacing a method call with another
# module_A.py
def original_func(arg_a,arg_b):
    # ...

# module_B.py
import module_A

def func_under_test():
    # ...
    module_A.original_func(a,b)
    # Some code that depends on the behavior of the patched function
    # ...

# my test code
def alternative_func(arg_a,arg_b):
    # do something essential for the test

def the_test():
    # patch the original_func with the alternative_func here
    func_under_test()
    # assertions

module_A.original_func = alternative_func

import module_a

def the_test():
    orig_func = module_a.original_func
    module_a.original_func = alternative_func

    # do testing stuff

    # then restore original func for other tests
    module_a.original_func = orig_func

original_func = alternative_func