No signals were fired

Raise code

        def add(self, *args, **kwargs):
            ''' The actual handler of the signal. '''
            self.heard.append((args, kwargs))

        def assert_heard_one(self, *args, **kwargs):
            ''' The signal fired once, and with the arguments given '''
            if len(self.heard) == 0:
                raise AssertionError('No signals were fired')
            elif len(self.heard) > 1:
                msg = '{0} signals were fired'.format(len(self.heard))
                raise AssertionError(msg)
            elif self.heard[0] != (args, kwargs):
                msg = 'One signal was heard, but with incorrect arguments: '\
                    'Got ({0}) expected ({1}, {2})'
                raise AssertionError(msg.format(self.heard[0], args, kwargs))