See #25748 (comment):
"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".
665c774#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 4f72526 by Erlend Egeberg Aasland in branch 'main':
bpo-43988: Add test.support.check_disallow_instantiation() (GH-25757)
4f72526

New changeset fbff538 by Erlend Egeberg Aasland in branch 'main':
bpo-43988: Use check disallow instantiation helper (GH-26392)
fbff538

New changeset 8cec740 by Erlend Egeberg Aasland in branch 'main':
bpo-43988: Document test.support.check_disallow_instantiation() (GH-26394)
8cec740

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 0a3452e by Erlend Egeberg Aasland in branch '3.10':
[3.10] bpo-43988: Add test.support.check_disallow_instantiation() (GH-25757) (GH-26885)
0a3452e

New changeset 9049ea5 by Erlend Egeberg Aasland in branch 'main':
bpo-43988: Fix test.support.check_disallow_instantiation version added (GH-26889)
9049ea5