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See https://github.com/python/cpython/pull/25748#discussion_r623849521:
"What do you think of adding support.assert_disallow_instanciation(type, *args) function which would check for TypeError but also check the error message? TypeError is quite generic and it might hide a bug."
Ref. bpo-43916.

You can take this issue as an opportunity to fix my typo :-)
Lib/test/test_hashlib.py: "test_disallow_instanciation" => "test_disallow_instantiation".
https://github.com/python/cpython/commit/665c7746fca180266b121183c2d5136c547006e0#commitcomment-50235589
There are now many tests:
Lib/test/test_array.py: def test_disallow_instantiation(self):
Lib/test/test_curses.py: def test_disallow_instantiation(self):
Lib/test/test_dbm_gnu.py: def test_disallow_instantiation(self):
Lib/test/test_embed.py: def test_disallow_instantiation(self):
Lib/test/test_functools.py: def test_disallow_instantiation(self):
Lib/test/test_hashlib.py: def test_disallow_instanciation(self):
Lib/test/test_hashlib.py: def test_hash_disallow_instanciation(self):
Lib/test/test_re.py: def test_disallow_instantiation(self):
Lib/test/test_select.py: def test_disallow_instantiation(self):
Lib/test/test_threading.py: def test_disallow_instantiation(self):
Lib/test/test_unicodedata.py: def test_disallow_instantiation(self):
Lib/test/test_zlib.py: def test_disallow_instantiation(self):

I'll fix your typo ;) I'll include the rest of the test in the PR. I just pushed it out quickly to get a review of the solution.

You can keep PR 25757 to add the helper function, and then write a second PR to use it in all tests.

New changeset 4f725261c6cf23d259e8fdc205e12b76ef4d2d31 by Erlend Egeberg Aasland in branch 'main':
bpo-43988: Add test.support.check_disallow_instantiation() (GH-25757)
https://github.com/python/cpython/commit/4f725261c6cf23d259e8fdc205e12b76ef4d2d31

New changeset fbff5387c3e1f3904420fa5a27738c6c5881305b by Erlend Egeberg Aasland in branch 'main':
bpo-43988: Use check disallow instantiation helper (GH-26392)
https://github.com/python/cpython/commit/fbff5387c3e1f3904420fa5a27738c6c5881305b

New changeset 8cec740820fc875117bfa7b6bdb10202ebeb8fd5 by Erlend Egeberg Aasland in branch 'main':
bpo-43988: Document test.support.check_disallow_instantiation() (GH-26394)
https://github.com/python/cpython/commit/8cec740820fc875117bfa7b6bdb10202ebeb8fd5

I believe we can close this now, Victor. Please reopen if you disagree :)

> I believe we can close this now, Victor. Please reopen if you disagree :)
I validated that all tests named "test(...)disallow(...)inst(...)" are now using support.check_disallow_instantiation().
Lib/test/test_tcl.py might use it in:
 @support.cpython_only
 def test_new_tcl_obj(self):
 self.assertRaises(TypeError, _tkinter.Tcl_Obj)
 self.assertRaises(TypeError, _tkinter.TkttType)
 self.assertRaises(TypeError, _tkinter.TkappType)
Serhiy suggested to write an unit test for curses.ncurses_version:
https://bugs.python.org/issue43916#msg391936
This work can be done in bpo-43916.

> Lib/test/test_tcl.py might use it [...]
Absolutely.
> Serhiy suggested to write an unit test for curses.ncurses_version:
> https://bugs.python.org/issue43916#msg391936
>
> This work can be done in bpo-43916.
All right.

New changeset 0a3452e7cf00c51ab1af0f674b670520b09f0e39 by Erlend Egeberg Aasland in branch '3.10':
[3.10] bpo-43988: Add test.support.check_disallow_instantiation() (GH-25757) (GH-26885)
https://github.com/python/cpython/commit/0a3452e7cf00c51ab1af0f674b670520b09f0e39

New changeset 9049ea51eca081984c8ae37dfeb68b75d624e90d by Erlend Egeberg Aasland in branch 'main':
bpo-43988: Fix test.support.check_disallow_instantiation version added (GH-26889)
https://github.com/python/cpython/commit/9049ea51eca081984c8ae37dfeb68b75d624e90d