def test_basicFormat(self):
        event = dict(log_format="Hello, {who}!", who="dude")
        records, output = self.logEvent(event)

        self.assertEqual(len(records), 1)
        self.assertEqual(str(records[0].msg), u"Hello, dude!")
        self.assertEqual(records[0].args, ())
Basic formattable event passes the format along correctly.
dataset/ETHPy150Open twisted/twisted/twisted/logger/test/test_stdlib.py/STDLibLogObserverTests.test_basicFormat