Python mockito - how to mock instance creation

Question

I want to mock a class constructor in Python via mockito, ie return a Mock-class instance instead of the real one. Assuming you have an import statement in the form

from my.module import SomeClass

How can this be done? I've seen https://code-and-cocktails.herokuapp.com/blog/2015/01/19/mocking-class-constructor-in-python-with-mockito/ , which suggests

when(my.module).SomeClass().thenReturn(someFakeInstance)

however, this doesn't work with above's import statement for me; it only works when doing "import my.module" and instantiating via "my.module.SomeClass()".

Are there any viable solutions that work with the import statement above?

Thanks

Answer 1

What you tried is in general how it works, but since you do a deep import patching my.module is not want you want. You want to patch the module this code lives in. Say it is in a file module_under_test.py where you have

from x.y import SomeClass

Now, from the tests you look at it differently:

import module_under_test as mut

Now SomeClass is at mut.SomeClass , hence in the test you mock

when(mut).SomeClass(...)

This is super-confusing the first couple of times you're doing this, but not very special to mockito but how python works.