Mocking a subprocess call in Python
Question: I have a method (`run_script`) would like to test. Specifically I want to test
that a call to `subprocess.Popen`occurs. It would be even better to test that
`subprocess.Popen` is called with certain parameters. When I run the test
however I get `TypeError: 'tuple' object is not callable`.

How can I test my method to ensure that **subprocess** is actually being
called using mocks?

    
    
    @mock.patch('subprocess.Popen')
    def run_script(file_path):
      process = subprocess.Popen(['myscript', -M, file_path], stdout=subprocess.PIPE)
      output,err = process.communicate()
      return process.returncode
    
    def test_run_script(self, mock_subproc_popen):
      mock_subproc_popen.return_value = mock.Mock(communicate=('ouput','error'), returncode=0)
      am.account_manager("path")
      self.assertTrue(mock_subproc_popen.called)
    


Answer: It seems unusual to me that you use the patch decorator over the `run_script`
function, since you don't pass a mock argument there.

How about this:

    
    
    def run_script(file_path):
      process = subprocess.Popen(['myscript', -M, file_path], stdout=subprocess.PIPE)
      output,err = process.communicate()
      return process.returncode
    
    @mock.patch('subprocess.Popen')
    def test_run_script(self, mock_subproc_popen):
      process_mock = mock.Mock()
      attrs = {'communicate.return_value': ('output', 'error')}
      process_mock.configure_mock(**attrs)
      mock_subproc_popen.return_value = process_mock 
      am.account_manager("path") # this calls run_script somewhere, is that right?
      self.assertTrue(mock_subproc_popen.called)
    

Right now, your mocked subprocess.Popen seems to return a tuple, causeing
process.communicate() to raise `TypeError: 'tuple' object is not callable.`.
Therefore it's most important to get the return_value on mock_subproc_popen
just right.

