Q:

Python SafeConfigParser mocking

I'm studying how to use mocking in my unit test program.
Now I have a SafeConfigParser object and I want to test what I write is correct.
After google the mocking usage of SafeConfigParser, I already know how to test the read of SafeConfigParser. But I still don't know how to verify the write of SafeConfigParser.
My idea is:

Make a empty buffer.
Consider a method that can set the buffer to SafeConfigParser.
Call the function which include SafeConfigParser.write()
Verify the buffer with my answer.

My program which need to be tested is like following:
def write_tokens_to_config(self):
    """Write token values to the config
    """

    parser = SafeConfigParser()
    with open(self.CONFIG_PATH) as fp:
        parser.readfp(fp)
        if not parser.has_section('Token'):
            parser.add_section('Token')
    parser.set('Token', 'access_token', self._access_token)
    parser.set('Token', 'refresh_token', self._refresh_token)
    with open(self.CONFIG_PATH, 'wb') as fp:
        parser.write(fp)

P.S. You can check the read part from this url: http://www.snip2code.com/Snippet/4347/

A:

I finally find out a solution :).
I modify my program(ex: program.py) to the followings:
class Program(): 

    def __init__(self):
        self._access_token = None
        self._refresh_token = None
        self.CONFIG_PATH = 'test.conf'

    def write_tokens_to_config(self):
        """Write token value to the config
        """

        parser = SafeConfigParser()
        parser.read(self.CONFIG_PATH)
        if not parser.has_section('Token'):
            parser.add_section('Token')
        parser.set('Token', 'access_token', self._access_token)
        parser.set('Token', 'refresh_token', self._refresh_token)
        with open(self.CONFIG_PATH, 'wb') as f:
            parser.write(f)

And my test program like this:
class TestMyProgram(unittest.TestCase):

    def setUp(self):
        from program import Program
        self.program = Program()

    def test_write_tokens_to_config(self):
        from mock import mock_open
        from mock import call
        self.program._access_token = 'aaa'
        self.program._refresh_token = 'bbb'
        with mock.patch('program.ConfigParser.SafeConfigParser.read'):
            m = mock_open()
            with mock.patch('__builtin__.open', m, create=True):
                self.program.write_tokens_to_config()
                m.assert_called_once_with(self.program.CONFIG_PATH, 'wb')
                handle = m()
                handle.write.assert_has_calls(
                    [
                        call('[Token]\n'),
                        call('access_token = aaa\n'),
                        call('refresh_token = bbb\n'),
                    ]
                )

Ref: http://docs.python.org/dev/library/unittest.mock#mock-open

