python mock, patch example

my_class.py

from third_party_lib import make_service, make_credentials


class MyClass(object):

    @classmethod
    def from_json(cls, json):
        credentials = make_credentials(json)
        return cls(credentials)

    def __init__(self, credentials):
        self.credentials = credentials

    def _service(self):
        return make_service(self.credentials)

    def a_method(self, credential_id):
        request_obj = self._service().get(credential_id)
        result = request_obj.execute()
        values = result.get('values', [])
        return values

ref.md

• http://www.voidspace.org.uk/python/mock/patch.html#where-to-patch
• http://www.voidspace.org.uk/python/mock/mock.html?highlight=propertymock#mock.PropertyMock
• https://qiita.com/FGtatsuro/items/eb2b05ff56f3599a1248
• http://thinkami.hatenablog.com/entry/2017/03/17/062138

test_my_class.py

import unittest
from unittest.mock import MagicMock, patch

from my_class import MyClass


class TestMyClass(unittest.TestCase):
    def test_from_json(self):
        with patch('my_class.make_credentials') as mock:
            mock.side_effect = Exception('Boom!')
            with self.assertRaises(Exception) as ctx:
                my_obj = MyClass.from_json('this is not json')
            the_exc = ctx.exception
            self.assertIsInstance(the_exc, Exception)
            self.assertEqual(str(the_exc), 'Boom!')

    @patch('my_class.make_credentials')
    @patch('third_party_lib.Service')
    def test_a_method(self,
                      mock_service,
                      mock_make_credentials):
        mock_service.return_value.get.return_value.execute.return_value = {'values': [['row_1']]}

        my_obj = MyClass.from_json('this is not json')
        rows = my_obj.a_method(credential_id=22)
        self.assertEqual(rows[0][0], 'row_1')

if __name__ == "__main__":
    unittest.main()

third_party_lib.py

class Service(object):
    """some service"""


class Auth(object):
    """some auth"""


def make_service(credentials):
    return Service(credentials)


def make_credentials(json):
    return Auth(json)