上下文
我正在尝试使用加密库进行pytest。在测试中，我使用故意损坏的身份验证标记解密和验证某些数据。这样做应该引发"InvalidTag"异常，如以下示例中所述。
我使用以下方式使用 pytest 断言异常：
with pytest.raises(Exception, match='a_string'):
myfunc()
我的代码示例
#!/usr/bin/env python3
import pytest
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes
key = bytes.fromhex(
"1111111111111111111111111111111111111111111111111111111111111111")
iv = bytes.fromhex("222222222222222222222222")
aad = bytes.fromhex("33333333333333333333333333333333")
pt = bytes.fromhex("4444444444444444")
def myfunc():
raise ValueError("Exception 123 raised")
def test_match():
with pytest.raises(ValueError, match=r".* 123 .*"):
myfunc()
def decrypt():
# encrypt
encryptor = Cipher(
algorithms.AES(key),
modes.GCM(iv),
backend=default_backend()
).encryptor()
encryptor.authenticate_additional_data(aad)
ct = encryptor.update(pt) + encryptor.finalize()
tag = encryptor.tag
# let us corrupt the tag
corrupted_tag = bytes.fromhex("55555555555555555555555555555555")
# decrypt
decryptor = Cipher(
algorithms.AES(key),
modes.GCM(iv, corrupted_tag),
backend=default_backend()
).decryptor()
decryptor.authenticate_additional_data(aad)
return decryptor.update(ct) + decryptor.finalize()
def test_decrypt():
with pytest.raises(Exception, match='InvalidTag'):
decrypt()
这里真正重要的是函数 test_decrypt((。目前，如果我使用以前的代码运行pytest，我会得到以下输出：
> ▶ pytest
>
> ============================================== test session starts ===============================================
> platform darwin -- Python 3.8.2, pytest-5.4.2, py-1.8.1, pluggy-0.13.1
> rootdir: somewhere
> collected 2 items
>
> tests/test_pytest_exception.py .F [100%]
>
> ==================================================== FAILURES ====================================================
> __________________________________________________ test_decrypt __________________________________________________
>
> def test_decrypt():
> with pytest.raises(Exception, match='InvalidTag'):
> > decrypt()
>
> tests/test_pytest_exception.py:52:
> _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
>
> def decrypt():
> # encrypt
> encryptor = Cipher(
> algorithms.AES(key),
> modes.GCM(iv),
> backend=default_backend()
> ).encryptor()
> encryptor.authenticate_additional_data(aad)
> ct = encryptor.update(pt) + encryptor.finalize()
> tag = encryptor.tag
>
> # let us corrupt the tag
>
> corrupted_tag = bytes.fromhex("55555555555555555555555555555555")
>
> # decrypt
> decryptor = Cipher(
> algorithms.AES(key),
> modes.GCM(iv, corrupted_tag),
> backend=default_backend()
> ).decryptor()
> decryptor.authenticate_additional_data(aad)
>
> > return decryptor.update(ct) + decryptor.finalize()
>
> tests/test_pytest_exception.py:47:
> _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
>
> self = <cryptography.hazmat.primitives.ciphers.base._AEADCipherContext object at 0x10d2d53a0>
>
> def finalize(self):
> if self._ctx is None:
> raise AlreadyFinalized("Context was already finalized.")
> > data = self._ctx.finalize()
>
> ../../../.local/share/virtualenvs/a_virtual_env/lib/python3.8/site-packages/cryptography/hazmat/primitives/ciphers/base.py:198:
> _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
>
> self = <cryptography.hazmat.backends.openssl.ciphers._CipherContext object at 0x10d2d5040>
>
> def finalize(self):
> # OpenSSL 1.0.1 on Ubuntu 12.04 (and possibly other distributions)
> # appears to have a bug where you must make at least one call to update
> # even if you are only using authenticate_additional_data or the
> # GCM tag will be wrong. An (empty) call to update resolves this
> # and is harmless for all other versions of OpenSSL.
> if isinstance(self._mode, modes.GCM):
> self.update(b"")
>
> if (
> self._operation == self._DECRYPT and
> isinstance(self._mode, modes.ModeWithAuthenticationTag) and
> self.tag is None
> ):
> raise ValueError(
> "Authentication tag must be provided when decrypting."
> )
>
> buf = self._backend._ffi.new("unsigned char[]", self._block_size_bytes)
> outlen = self._backend._ffi.new("int *")
> res = self._backend._lib.EVP_CipherFinal_ex(self._ctx, buf, outlen)
> if res == 0:
> errors = self._backend._consume_errors()
>
> if not errors and isinstance(self._mode, modes.GCM):
> > raise InvalidTag
> E cryptography.exceptions.InvalidTag
>
> ../../../.local/share/virtualenvs/a_virtual_env/lib/python3.8/site-packages/cryptography/hazmat/backends/openssl/ciphers.py:170: InvalidTag
>
> During handling of the above exception, another exception occurred:
>
> def test_decrypt():
> with pytest.raises(Exception, match='InvalidTag'):
> > decrypt()
> E AssertionError: Pattern 'InvalidTag' does not match ''
>
> tests/test_pytest_exception.py:52: AssertionError
> ============================================ short test summary info =============================================
> FAILED tests/test_pytest_exception.py::test_decrypt - AssertionError: Pattern 'InvalidTag' does not match ''
> ========================================== 1 failed, 1 passed in 0.12s ===========================================
从此输出来看，似乎提出了"InvalidTag"异常，但第二个异常也是出于我不明白的原因。 如果我不运行测试，但我只是运行函数 decrypt((，我会得到以下输出：
> python3 tests/test_pytest_exception.py
> Traceback (most recent call last):
> File "tests/test_pytest_exception.py", line 54, in <module>
> decrypt()
> File "tests/test_pytest_exception.py", line 47, in decrypt
> return decryptor.update(ct) + decryptor.finalize()
> File "somewhere/a_virtual_env/lib/python3.8/site-packages/cryptography/hazmat/primitives/ciphers/base.py", line 198, in finalize
> data = self._ctx.finalize()
> File "somewhere/a_virtual_env/lib/python3.8/site-packages/cryptography/hazmat/backends/openssl/ciphers.py", line 170, in finalize
> raise InvalidTag
> cryptography.exceptions.InvalidTag
从这个输出中，我毫不怀疑会引发"无效标签"异常。
问题
我想检查在使用 pytest 的单元测试中是否引发"无效标签"异常以通过测试。 根据我之前解释的，我做错了什么？
要pytest.raises()的match参数对异常的字符串表示形式执行正则表达式匹配，这不是您想要的。
相反，只需将cryptography.exceptions.InvalidTag类型作为第一个参数传递：
from cryptography.exceptions import InvalidTag
...
def test_decrypt():
with pytest.raises(InvalidTag):
decrypt()
你检查的方式错误。您正在验证一般异常，并尝试匹配错误消息，而不是实际异常。我认为它应该是这样的：
from cryptography.exceptions import InvalidTag
def test_decrypt():
with pytest.raises(InvalidTag, match=''):
decrypt()