Mocking Files In Python Unittest In Imported Modules

Question

I readily admit to going a bit overboard with unit testing. While I have passing tests, I find my solution to be inelegant, and I'm curious if anyone has a cleaner solution.

The class being tested:

class Config():

    def __init__(self):
        config_parser = ConfigParser()
        try:
            self._read_config_file(config_parser)
        except FileNotFoundError as e:
            pass

        self.token = config_parser.get('Tokens', 'Token', )

    @staticmethod
    def _read_config_file(config):
        if not config.read(os.path.abspath(os.path.join(BASE_DIR, ROOT_DIR, CONFIG_FILE))):
            raise FileNotFoundError(f'File {CONFIG_FILE} not found at path {BASE_DIR}{ROOT_DIR}')

The ugly test:

class TestConfiguration(unittest.TestCase):

    @mock.patch('config.os.path.abspath')
    def test_config_init_sets_token(self, mockFilePath: mock.MagicMock):
        with open('mock_file.ini', 'w') as file: #here's where it gets ugly
            file.write('[Tokens]\nToken: token')
        mockFilePath.return_value = 'mock_file.ini'

        config = Config()

        self.assertEqual(config.token, 'token')
        os.remove('mock_file.ini') #quite ugly

EDIT: What I mean is I'm creating a file instead of mocking one. Does anyone know how to mock a file object, while having its data set so that it reads ascii text? The class is deeply buried. Other than that, the way ConfigParser sets data with .read() is throwing me off. Granted, the test "works", it doesn't do it nicely.

For those asking about other testing behaviors, here's an example of another test in this class:

@mock.patch('config.os.path.abspath')
def test_warning_when_file_not_found(self, mockFilePath: mock.MagicMock):
    mockFilePath.return_value = 'mock_no_file.ini'

    with self.assertRaises(FileNotFoundError):
        config.Config._read_config_file(ConfigParser())

Thank you for your time.

Answer 1

I've found it!

I had to start off with a few imports:from io import TextIOWrapper, BytesIO

This allows a file object to be created: TextIOWrapper(BytesIO(b'<StringContentHere>'))

The next part involved digging into the configparser module to see that it calls open(), in order to mock.patch the behavior, and, here we have it, an isolated unittest!

@mock.patch('configparser.open') 
def test_bot_init_sets_token(self, mockFileOpen: mock.MagicMock):

    mockFileOpen.return_value = TextIOWrapper(BytesIO(b'[Tokens]\nToken: token'))

    config = Config()

    self.assertEqual(config.token, 'token')