如何使用 pytest raises 检查异常原因？

Question

I'd like to test that an exception is raised from another exception type.

import pytest


def throw_with_cause():
  raise Exception("Failed") from ValueError("That was unexpected.")
 
with pytest.raises(Exception): # from ValueError???
  throw_with_cause()

I'm surprised not to see a way to inspect the exception chain in the pytest raises docs. https://docs.pytest.org/en/6.2.x/reference.html#pytest-raises

Is there a clean way to do this using ptyest raises?

Answer 1

Until something more readable comes along, I'm doing the following.

import pytest

def throw_with_cause():
   raise Exception("Failed") from ValueError("That was unexpected.")


def test_throws_with_cause():
    with pytest.raises(Exception, match="Failed") as exc_info:
        throw_with_cause()
    assert type(exc_info.value.__cause__) is ValueError