def test_outFile(self):
        """
        Returned L{FileLogObserver} has the correct outFile.
        """
        with StringIO() as fileHandle:
            observer = textFileLogObserver(fileHandle)
            self.assertIs(observer._outFile, fileHandle)

        Returned L{FileLogObserver} has the correct outFile.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/logger/test/test_file.py