I have a function that uses callLater extensively to schedule a number of different tasks. I don't want to get into the rationale behind such a design, but here is a contrived example which will help me explain my problem: 

    def b():

        '''Do some work'''

    def c():

        '''Do some more work'''

    def a(flag):

        if flag:

            return Reactor.callLater(300, b)

        else:

            return Reactor. callLater(100, c)

Now I want to test this function. Of course I can't wait for 5 minutes to ensure that `b` or `c` will indeed be called. What I need is some sort of mock clock which lets me fast forward time. Does any such thing exist in Twisted / Trial? Or is there any other approach to test such code?

Regards

Shakkhar