doctest: Allow checking for Traceback context errors

Feature or enhancement

Proposal:

If the error thrown in a doctest command is a ValueError, and that error object has a __context__ of RuntimeError, it would be nice to be able to do this:

>>> function_that_raises()
Traceback (most recent call last):
  ...
RuntimeError

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  ...
ValueError

And a similar thing for __cause__ but with the different line of text in the middle.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

I did make a discourse post, but it only got a like and no comments :)

從 doctest 的 traceback 檢查實作及其現有測試開始；該 issue 未提供檔案路徑。重現所示的 context 情況，並將其與提議的 cause 變體進行比較，然後為所要求的中間 traceback 文字新增覆蓋測試，並驗證 doctest 輸出。