The `unittest` `-b` command line option hides the output of `pdb`.

Bug report

Bug description:

import unittest

class Test(unittest.TestCase):
    def test(self):
        print("hello")
        breakpoint()
        print("goodbye")

If I invoke this like:

$ python3 -m unittest -b repo.py

Nothing is printed and the process sits waiting on input.

Whereas without the -b option we get the Pdb prompt:

$ python3 -m unittest repo.py 
hello
> /home/matthew/code/coveragepy_issue_1963/repo.py(7)test()
-> print("goodbye")
(Pdb) 

I would expect that the debugger prompt would not be swallowed up by the "-b" option, or that some error message would pop up saying that the "-b" option and the debugger were incompatible.

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Start by running the reported python3 -m unittest -b repo.py reproducer and compare it with the unbuffered command. Trace how unittest's -b output buffering interacts with breakpoint() and pdb, then add coverage for the interaction; done means the debugger prompt is usable or an explicit incompatibility error is produced.