def test_procFDImplementation(self):
        """
        L{_FDDetector._procFDImplementation} raises L{OSError} if there is no
        I{/proc/<pid>/fd} directory, otherwise it returns the basenames of its
        children interpreted as integers.
        """
        self.procfs = False
        self.assertRaises(OSError, self.detector._procFDImplementation)
        self.procfs = True
        self.assertEqual([0, 1, 2], self.detector._procFDImplementation())

        L{_FDDetector._procFDImplementation} raises L{OSError} if there is no
        I{/proc/<pid>/fd} directory, otherwise it returns the basenames of its
        children interpreted as integers.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_posixprocess.py