mock.patch() not patching class who called a couples of levels inside function call

Question

I have a task

def task():
   a = worker()
   a.do_some_work()

Worker itself is a separate class in separate module, who use Driver class like that,

class Worker(object):
   def __init__(self):
     self.driver = Driver(args)
     ...

and once again Driver is a separate class in separate module

so when I trying something like

with patch('package.module.Driver', new=Mock(return_value=999)):
   task()

in task there is still a Driver class instance, but not a mock. That's wrong. How to fix that?

UPD1: Driver and Worker live in different modules and Worker import Driver

`Driver` is a global in the module `Worker` lives in; are you patching *that global* or where the global was imported from? — Martijn Pieters, Aug 26 '14 at 15:13
See http://www.voidspace.org.uk/python/mock/patch.html#where-to-patch — Martijn Pieters, Aug 26 '14 at 15:13
But if you are unittesting `task` you may want to just mock the whole worker.. — Martijn Pieters, Aug 26 '14 at 15:13
@MartijnPieters Could I just patch only driver. It's important for me to make it work that way? — Ph0en1x, Aug 26 '14 at 15:15
From a testing philosophy point of view you'd mock the Worker; but if patching the driver is easier, then call it an integration test and be done with it. :-) — Martijn Pieters, Aug 26 '14 at 15:21
But I trying to path it in integration test, but patching not worked. That's why I'm asking) — Ph0en1x, Aug 26 '14 at 15:27
You didn't answer my question though; what is `package.module` here? Where does `Driver` live, and where does `Worker`? — Martijn Pieters, Aug 26 '14 at 15:28
Driver and Worker live in different modules and Worker import Driver — Ph0en1x, Aug 26 '14 at 15:30
You are not answering my question still. :-P Is `package.module` the module of the Driver then? — Martijn Pieters, Aug 26 '14 at 15:40
@MartijnPieters you could think about it that way: Worker = MyProject.Workers.base.Worker, Driver = MyProject.utils.drivers.Driver and yes, I'm using names of modules, where class actually defined — Ph0en1x, Aug 26 '14 at 15:44
So `package.module.Driver` here is `MyProject.utils.drivers.Driver`? — Martijn Pieters, Aug 26 '14 at 15:45
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/60015/discussion-between-ph0en1x-and-martijn-pieters). — Ph0en1x, Aug 26 '14 at 15:45

score 8 · Accepted Answer · answered Aug 26 '14 at 15:47

Your MyProject.Workers.base module imported Driver as a global:

from MyProject.utils.drivers import Driver

This is a new, separate reference to the Driver class. If you now patch MyProject.utils.drivers.Driver, the Worker class will not see the patched object; as it'll use it's own global reference.

Patch the global Worker actually uses:

with patch('MyProject.Workers.base.Driver', new=Mock(return_value=999)):
    task()

See the Where to patch section of the mock documentation.

mock.patch() not patching class who called a couples of levels inside function call

1 Answers1