Result of Override a “private” method in a python module

files.py

# module.py

def _cmd(command, args):
  # do something nasty
  print(command, args)

def function_to_be_tested():
  # do cool things
  _cmd('rm', '-rf /')
  return 1

# test.py

from mock import patch
import module

def _cmd_mock(command, args):
  # do nothing
  pass

@patch('module._cmd', _cmd_mock) 
def test_function():
  assert module.function_to_be_tested() == 1

# result

$ python test.py 
Nothing