'A C{_Traceback} object constructed with a single frame should be able
to be passed to L{traceback.extract_tb}, and we should get a singleton
list containing a (filename, lineno, methodname, line) tuple.'

def test_singleFrame(self):

    tb = failure._Traceback([['method', 'filename.py', 123, {}, {}]])
    self.assertEqual(traceback.extract_tb(tb), [_tb('filename.py', 123, 'method', None)])
