Hi, to make unittest more extensible and for issue 18765 (having a way to run pdb when tests fail), I would like to make TestCase aware of the command line arguments given to the TestProgram so they can adapt their behavior based on them.

I suggested this change on python-ideas (https://mail.python.org/pipermail/python-ideas/2019-March/055842.html) but it did not get much attention.

I'm opening a PR in the hope to get more feedback and will start writing documentation.

Please comment if this is not appropriate or regarding anything I might have not thought of.