How do I mock a django signal handler?

Question

I have a signal_handler connected through a decorator, something like this very simple one:

@receiver(post_save, sender=User, 
          dispatch_uid='myfile.signal_handler_post_save_user')
def signal_handler_post_save_user(sender, *args, **kwargs):
   # do stuff

What I want to do is to mock it with the mock library http://www.voidspace.org.uk/python/mock/ in a test, to check how many times django calls it. My code at the moment is something like:

def test_cache():
    with mock.patch('myapp.myfile.signal_handler_post_save_user') as mocked_handler:
        # do stuff that will call the post_save of User
    self.assert_equal(mocked_handler.call_count, 1)

The problem here is that the original signal handler is called even if mocked, most likely because the @receiver decorator is storing a copy of the signal handler somewhere, so I'm mocking the wrong code.

So the question: how do I mock my signal handler to make my test work?

Note that if I change my signal handler to:

def _support_function(*args, **kwargs):
    # do stuff

@receiver(post_save, sender=User, 
          dispatch_uid='myfile.signal_handler_post_save_user')
def signal_handler_post_save_user(sender, *args, **kwargs):
   _support_function(*args, **kwargs)

and I mock _support_function instead, everything works as expected.

Answer 1

Possibly a better idea is to mock out the functionality inside the signal handler rather than the handler itself. Using the OP's code:

@receiver(post_save, sender=User, dispatch_uid='myfile.signal_handler_post_save_user')
def signal_handler_post_save_user(sender, *args, **kwargs):
  do_stuff()  # <-- mock this

def do_stuff():
   ... do stuff in here

Then mock do_stuff:

with mock.patch('myapp.myfile.do_stuff') as mocked_handler:
    self.assert_equal(mocked_handler.call_count, 1)