'Install a no-op signal handler that can be set to allow
interrupts or not, and arrange for the original signal handler to be
re-installed when the test is finished.'

def setUp(self):

    self.signum = signal.SIGUSR1
    oldhandler = signal.signal(self.signum, (lambda x, y: None))
    self.addCleanup(signal.signal, self.signum, oldhandler)
