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=\'myfil         


        

Answer 1

There is a way to mock django signals with a small class.

You should keep in mind that this would only mock the function as a django signal handler and not the original function; for example, if a m2mchange trigers a call to a function that calls your handler directly, mock.call_count would not be incremented. You would need a separate mock to keep track of those calls.

Here is the class in question:

class LocalDjangoSignalsMock():
    def __init__(self, to_mock):
        """ 
        Replaces registered django signals with MagicMocks

        :param to_mock: list of signal handlers to mock
        """
        self.mocks = {handler:MagicMock() for handler in to_mock}
        self.reverse_mocks = {magicmock:mocked
                              for mocked,magicmock in self.mocks.items()}
        django_signals = [signals.post_save, signals.m2m_changed]
        self.registered_receivers = [signal.receivers
                                     for signal in django_signals]

    def _apply_mocks(self):
        for receivers in self.registered_receivers:
            for receiver_index in xrange(len(receivers)):
                handler = receivers[receiver_index]
                handler_function = handler[1]()
                if handler_function in self.mocks:
                    receivers[receiver_index] = (
                        handler[0], self.mocks[handler_function])

    def _reverse_mocks(self):
        for receivers in self.registered_receivers:
            for receiver_index in xrange(len(receivers)):
                handler = receivers[receiver_index]
                handler_function = handler[1]
                if not isinstance(handler_function, MagicMock):
                    continue
                receivers[receiver_index] = (
                    handler[0], weakref.ref(self.reverse_mocks[handler_function]))

    def __enter__(self):
        self._apply_mocks()
        return self.mocks

    def __exit__(self, *args):
        self._reverse_mocks()

Example usage

to_mock = [my_handler]
with LocalDjangoSignalsMock(to_mock) as mocks:
    my_trigger()
    for mocked in to_mock:
        assert(mocks[mocked].call_count)
        # 'function {0} was called {1}'.format(
        #      mocked, mocked.call_count)