Add `addCleanup` to `unittest.subTest`

Feature or enhancement

Proposal:

The unittest.subTest context (i.e. the object you get using with's as clause, currently None) should get methods to manage cleanups:

• addCleanup
• enterContext
• doCleanups

And similar ones for IsolatedAsyncIOTestCase.

They should do the same thing as the same methods on TestCase, but with subtest scope.
Example usage:

for param in 'a', 'b', 'c':
    with self.subTest() as sub:
        tempfile = make_tempfile()
        sub.addCleanup(os.unlink, tempfile)
        do_actual_test(tempfile, param)

See Discuss thread for motivation/discussion.

Has this already been discussed elsewhere?

I have already discussed this feature proposal on Discourse

Links to previous discussion of this feature:

https://discuss.python.org/t/unittest-add-addcleanup-to-subtest/91827

Linked PRs

• gh-134318

Comece pelos métodos de limpeza existentes de unittest.TestCase e pelo contexto unittest.subTest; em seguida, compare o comportamento correspondente de IsolatedAsyncIOTestCase. Leia a thread do Discourse e o PR vinculado gh-134318 para entender o escopo proposto. Considera-se concluído quando os métodos de limpeza solicitados funcionarem com o escopo de subtest tanto para casos síncronos quanto para casos assíncronos isolados.