I'm guessing you mean like: def has_expired(now=None): #.. implementation instead of: def has_expired(): #.. implementation But at s

I'm guessing you mean like: def has_expired(now=None): #.. implementation instead of: def has_expired(): #.. implementation But at some point you need to call that method somewhere else... def get_request_handler(request): #...code now = timezone.now() if has_expired(now=now): raise Error403. And `get_request_handler` still needs to be tested, which I 'stub' the API for getting the current time in the correct timezone within the test for the request. (Taking into account the other comment), using a library called 'mock'. (https://pypi.python.org/pypi/mock https://pypi.python.org/pypi/mock)