'L{TwistOptions.selectDefaultLogObserver} will not override an already
selected observer.'

def test_selectDefaultLogObserverDefaultWithTTY(self):

    class TTYFile(object, ):
        def isatty(self):
            return True
    self.patch(_options, 'stdout', TTYFile())
    options = TwistOptions()
    options.opt_log_file('-')
    options.selectDefaultLogObserver()
    self.assertIdentical(options['fileLogObserverFactory'], textFileLogObserver)
    self.assertEqual(options['logFormat'], 'text')
