def test_deferred(self):
        """
        C{_trimFrames} removes traces of C{_runCallbacks} when getting an error
        in a callback returned by a C{TestCase} based test.
        """
        test = erroneous.TestAsynchronousFail('test_fail')
        frames = self.getErrorFrames(test)
        self.checkFrames(frames,
                         [('_later', 'twisted/trial/test/erroneous')])

        C{_trimFrames} removes traces of C{_runCallbacks} when getting an error
        in a callback returned by a C{TestCase} based test.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/test/test_reporter.py