Mocking two functions with patch for a unit test

Question

I have a function I want to unit test contains calls two other functions. I am unsure how can I mock both functions at the same time properly using patch. I have provided an example of what I mean below. When I run nosetests, the tests pass but I feel that there must be a cleaner way to do this and I do not really Understand the piece regarding f.close()...

The directory structure looks like this:

program/   program/     data.py   tests/     data_test.py 

data.py:

import cPickle  def write_out(file_path, data):     f = open(file_path, 'wb')     cPickle.dump(data, f)     f.close() 

data_test.py:

from mock import MagicMock, patch  def test_write_out():     path = '~/collection'     mock_open = MagicMock()     mock_pickle = MagicMock()     f_mock = MagicMock()     with patch('__builtin__.open', mock_open):         f = mock_open.return_value         f.method.return_value = path         with patch('cPickle.dump', mock_pickle):             write_out(path, 'data')             mock_open.assert_called_once_with('~/collection', 'wb')             f.close.assert_any_call()             mock_pickle.assert_called_once_with('data', f) 

Results:

$ nosetests . ---------------------------------------------------------------------- Ran 1 test in 0.008s OK 

Answer 1

You can simplify your test by using the patch decorator and nesting them like so (they are MagicMock objects by default):

from unittest.mock import patch  @patch('cPickle.dump') @patch('__builtin__.open') def test_write_out(mock_open, mock_pickle):     path = '~/collection'     f = mock_open.return_value     f.method.return_value = path          write_out(path, 'data')          mock_open.assert_called_once_with('~/collection', 'wb')     mock_pickle.assert_called_once_with('data', f)     f.close.assert_any_call() 

Calls to a MagicMock instance return a new MagicMock instance, so you can check that the returned value was called just like any other mocked object. In this case f is a MagicMock named 'open()' (try printing f).