Python Unit Test Dictionary Assert KeyError

Question

I wasn't sure how to create a Python unittest to check if a dictionary returned a KeyError. I thought the unit test would call the dictionary key so it would look like this:

def test_dict_keyerror_should_appear(self):
    my_dict = {'hey': 'world'}
    self.assertRaises(KeyError, my_dict['some_key'])

However, my test would just error out with a KeyError instead of asserting that a KeyError occurred.

Looks like a dupe of http://stackoverflow.com/questions/11371849/testing-exception-message-with-assertraise#11371899 — Xavier C., Sep 22 '16 at 13:32

score 6 · Answer 1 · answered Sep 22 '16 at 13:26

6

To solve this I used a lambda to call the dictionary key to raise the error.

def test_dict_keyerror_should_appear(self):
    my_dict = {'hey': 'world'}
    self.assertRaises(KeyError, lambda: my_dict['some_key'])

answered Sep 22 '16 at 13:26

Will

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score 2 · Answer 2 · answered Sep 22 '16 at 13:33

2

Another option would be to use operator.getitem:

from operator import getitem

self.assertRaises(KeyError, getitem, my_dict, 'some_key')

answered Sep 22 '16 at 13:33

alecxe

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Python Unit Test Dictionary Assert KeyError

2 Answers2