How to mock just the method inside the class

Question

Trying to write a testcase for my class based function. This is skeleton of my class

class Library(object):
    def get_file(self):
        pass

    def query_fun(self):
        pass

    def get_response(self):
        self.get_file()

        response = self.query_fun()

        # some business logic here
        return response

I need to create a testcase that can mock just the query_fun and do the rest. tried below but seems is not the right direction:

from unittest import mock, TestCase
from library.library import Library

class TestLibrary(TestCase):
    def setUp(self):
        self.library = Library()

    @mock.patch('library.library.Library')
    def test_get_response(self, MockLibrary):
        mock_response = {
            'text': 'Hi',
            'entities': 'value',
        }
        MockLibrary.query_fun.return_value = mock_response
        response = MockLibrary.get_response()
        self.assertEqual(response, mock_response)

What I'm expecting is to setup mock and calling get_response will not actually call the original query_fun method, but instead call the mock query_fun.

Answer 1

You need to take into account you mocked the whole class. You can mock individual methods too:

@mock.patch('library.library.Library.query_fun')
def test_get_response(self, mock_query_fun):
    mock_query_fun.return_value = {
        'text': 'Hi',
        'entities': 'value'
        }
    }
    response = MockBotter.get_response()
    self.assertIsNotNone(response)

Only Library.query_fun has been replaced, everything else in the class is still in place.

Simplified demo:

>>> from unittest import mock
>>> class Library(object):
...     def query_fun(self):
...         pass
...     def get_response(self):
...         return self.query_fun()
...
>>> with mock.patch('__main__.Library.query_fun') as mock_query_fun:
...     mock_query_fun.return_value = {'foo': 'bar'}
...     print(Library().get_response())
...
{'foo': 'bar'}