Mocking two functions with patch for a unit test

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

@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).

In addition to the response @Matti John you can also use patch inside function test_write_out:

from mock import MagicMock, patchdef test_write_out():    path = '~/collection'    with patch('__builtin__.open') as mock_open, \            patch('cPickle.dump') as mock_pickle:        f = mock_open.return_value        ...

Here's a simple example on how to test raising ConflictError in create_collection function using mock:

import osfrom unittest import TestCasefrom mock import patchfrom ..program.data import ConflictError, create_collectionclass TestCreateCollection(TestCase):    def test_path_exists(self):        with patch.object(os.path, 'exists') as mock_method:            mock_method.return_value = True            self.assertRaises(ConflictError, create_collection, 'test')

Please, also see mock docs and Michael Foord's awesome introduction to mock.