Mocking a function to raise an Exception to test an except block

I have a function (foo) which calls another function (bar). If invoking bar() raises an HttpError, I want to handle it specially if the status code is 404, otherwise re-raise.

I am trying to write some unit tests around this foo function, mocking out the call to bar(). Unfortunately, I am unable to get the mocked call to bar() to raise an Exception which is caught by my except block.

Here is my code which illustrates my problem:

import unittest
import mock
from apiclient.errors import HttpError


class FooTests(unittest.TestCase):
    @mock.patch('my_tests.bar')
    def test_foo_shouldReturnResultOfBar_whenBarSucceeds(self, barMock):
        barMock.return_value = True
        result = foo()
        self.assertTrue(result)  # passes

    @mock.patch('my_tests.bar')
    def test_foo_shouldReturnNone_whenBarRaiseHttpError404(self, barMock):
        barMock.side_effect = HttpError(mock.Mock(return_value={'status': 404}), 'not found')
        result = foo()
        self.assertIsNone(result)  # fails, test raises HttpError

    @mock.patch('my_tests.bar')
    def test_foo_shouldRaiseHttpError_whenBarRaiseHttpErrorNot404(self, barMock):
        barMock.side_effect = HttpError(mock.Mock(return_value={'status': 500}), 'error')
        with self.assertRaises(HttpError):  # passes
            foo()

def foo():
    try:
        result = bar()
        return result
    except HttpError as error:
        if error.resp.status == 404:
            print '404 - %s' % error.message
            return None
        raise

def bar():
    raise NotImplementedError()

I followed the Mock docs which say that you should set the side_effect of a Mock instance to an Exception class to have the mocked function raise the error.

I also looked at some other related StackOverflow Q&As, and it looks like I am doing the same thing they are doing to cause and Exception to be raised by their mock.

• http://ift.tt/1uUvMeW


• How to use Python Mock to raise an exception - but with Errno set to a given value

Why is setting the side_effect of barMock not causing the expected Exception to be raised? If I am doing something weird, how should I go about testing logic in my except block?