python 3中的测试错误消息

Question

我有以下测试方法

def test_fingerprintBadFormat(self):
    """
    A C{BadFingerPrintFormat} error is raised when unsupported
    formats are requested.
    """
    with self.assertRaises(keys.BadFingerPrintFormat) as em:
        keys.Key(self.rsaObj).fingerprint('sha256-base')
    self.assertEqual('Unsupported fingerprint format: sha256-base',
        em.exception.message)

下面是exception类。

class BadFingerPrintFormat(Exception):
    """
    Raises when unsupported fingerprint formats are presented to fingerprint.
    """

此测试方法在Python2中运行良好，但在Python3中失败，并显示以下消息

builtins.AttributeError: 'BadFingerPrintFormat' object has no attribute 'message'

如何在Python3中测试错误消息。我不喜欢使用asserRaisesRegex的想法，因为它测试正则表达式而不是异常消息。

Answer 1

已从Python3中的异常中删除了.message属性。请改用.args[0]：

self.assertEqual('Unsupported fingerprint format: sha256-base',
    em.exception.args[0])

或者使用str(em.exception)获得相同的值：

self.assertEqual('Unsupported fingerprint format: sha256-base',
    str(em.exception))

这在Python 2和Python 3上都有效：

>>> class BadFingerPrintFormat(Exception):
...     """
...     Raises when unsupported fingerprint formats are presented to fingerprint.
...     """
...
>>> exception = BadFingerPrintFormat('Unsupported fingerprint format: sha256-base')
>>> exception.args
('Unsupported fingerprint format: sha256-base',)
>>> exception.args[0]
'Unsupported fingerprint format: sha256-base'
>>> str(exception)
'Unsupported fingerprint format: sha256-base'