python - mocking subprocess Process terminate -

i couldn't find question one. i'm having difficulty understanding how mock out returned value of subprocess.popen can validate terminate called when try stop it. server.py class looks this:

import os import subprocess  class server(object):      def start(self):         devnull = open(os.devnull, 'w')         self.proc = subprocess.popen(['python', '-c', 'import time; time.sleep(10);print "this message should not appear"'], stdout=devnull, stderr=devnull)      def stop(self):         if self.proc:             self.proc.terminate() 

my test class looks this. want know terminate called when stop called when run test nose says terminate called 0 times. understanding of patch replaces implementation of subprocess.popen , available methods.

from unittest import testcase server import server mock import patch, magicmock, mock  class servertest(testcase):      @patch("subprocess.popen")     @patch('__builtin__.open')     def test_stop_when_running(self, mock_open, mock_subprocess):         server = server()         server.start()         server.stop()         mock_subprocess.terminate.assert_called_once_with() 

you need mock popen that's used code you're testing. patch path be:

@patch("server.subprocess.popen") @patch('server.__builtin__.open') def test_stop_when_running(self, mock_open, mock_subprocess):     server = server()     server.start()     server.stop()     mock_subprocess.terminate.assert_called_once_with() 

however, terminate called on return value of subprocess.popen() need become:

mock_subprocess.return_value.terminate.assert_called_once_with()