Mocking open(file_name) in unit tests

Question

I have a source code that opens a csv file and sets up a header to value association. The source code is given below:

def ParseCsvFile(source): 
  \"\"\"Pa         


        

Answer 1

This is admittedly an old question, hence some of the answers are outdated.

In the current version of the mock library there is a convenience function designed for precisely this purpose. Here's how it works:

>>> from mock import mock_open
>>> m = mock_open()
>>> with patch('__main__.open', m, create=True):
...     with open('foo', 'w') as h:
...         h.write('some stuff')
...
>>> m.mock_calls
[call('foo', 'w'),
 call().__enter__(),
 call().write('some stuff'),
 call().__exit__(None, None, None)]
>>> m.assert_called_once_with('foo', 'w')
>>> handle = m()
>>> handle.write.assert_called_once_with('some stuff')

Documentation is here.