There are a lot of test cases in test_typing.py where we test that different typing things cannot be used as base classes. However, there are multiple missing cases. Examples:

• Final / Final[int] is not tested to be invalid base class:

  cpython/Lib/test/test_typing.py

  Lines 3748 to 3756 in 53a54b7

  	def test_cannot_subclass(self):
  	with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
  	class C(type(Final)):
  	pass
  	with self.assertRaisesRegex(TypeError, CANNOT_SUBCLASS_TYPE):
  	class C(type(Final[int])):
  	pass
  	def test_cannot_init(self):

• Ts is tested, but *Ts is not:

  cpython/Lib/test/test_typing.py

  Line 1039 in 53a54b7

  class C(Ts): pass

• Different special forms only tested with / or without []
• And other issues

I think this should be all covered. I went through all subtyping tests and added more cases.
I will send a PR :)