Can I fake/mock the type of my mock objects in python unittests

Question

In my python code I check the type of one of the parameters to make sure it is of the type I expect. For instance:

def myfunction(dbConnection):
    if (type(dbConnection)<>bpgsql.Connection):
        r['error'] += ' invalid database connection'

I want to pass a mock connection for testing purposes. Is there a way to make the mock object pretend to be of the correct type?

Asked By: Ali

||

Source

Answer 1

This is more-or-less exactly why you shouldn’t enforce strict typechecking! You should remove that line from the code entirely.

If you don’t want to do that, write an abstract base class with the properties you want to have (.connect(), .cursor(), …?) and check isinstance of that.

_{Also <> has been obsolete for aaages. Use !=.}

Answered By: Katriel

Answer 2

With all due respect, It looks like you guys are not quite correct!

I can use duck typing as said, but there is a way to do what I intended to do in the first place:

from http://docs.python.org/dev/library/unittest.mock.html

Mock objects that use a class or an instance as a spec or spec_set are able to pass isintance tests:

>>>
>>> mock = Mock(spec=SomeClass)
>>> isinstance(mock, SomeClass)
True
>>> mock = Mock(spec_set=SomeClass())
>>> isinstance(mock, SomeClass)
True

so my example code would be like:

m = mock.MagicMock(spec=bpgsql.Connection)
isinstance(m, bpgsql.Connection)

this returns True

All that said, I am not arguing for strict type checking in python, I say if you need to check it you can do it and it works with testing and mocking too.

Answered By: Ali

Can I fake/mock the type of my mock objects in python unittests

Question:

Answers: