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 :)

doctest の traceback チェック実装と既存のテストから始めてください。この issue にはファイルパスがありません。示されている context のケースを再現し、提案されている cause のバリアントと比較してから、要求された中間の traceback テキストのカバレッジを追加し、doctest の出力を確認してください。