'On instances that have a L{Logger} class attribute, the C{log_source}
key is available to format strings.'

def test_sourceAvailableForFormatting(self):

    obj = LogComposedObject('hello')
    log = obj.log
    log.error('Hello,    {log_source}.')
    self.assertIn('log_source', log.event)
    self.assertEqual(log.event['log_source'], obj)
    stuff = formatEvent(log.event)
    self.assertIn('Hello,    <LogComposedObject    hello>.', stuff)
