Add additional tests for new features in `typing.py`

[sobolevn]

BPO	46685
Nosy	@gvanrossum, @JelleZijlstra, @corona10, @miss-islington, @sobolevn, @Fidget-Spinner, @AlexWaygood
PRs	bpo-46685: improve test coverage of Self and Never in typing #31222 bpo-46685: cover TypeError of ForwardRef(1) in test_typing #31223 [3.10] bpo-46685: cover TypeError of ForwardRef(1) in test_typing (GH-31223) #31229 [3.9] bpo-46685: cover TypeError of ForwardRef(1) in test_typing (GH-31223) #31230

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2022-02-19.01:57:22.817>
created_at = <Date 2022-02-08.20:03:46.542>
labels = ['type-bug', 'tests', '3.11']
title = 'Add additional tests for new features in `typing.py`'
updated_at = <Date 2022-02-19.01:57:22.817>
user = 'https://github.com/sobolevn'

bugs.python.org fields:

activity = <Date 2022-02-19.01:57:22.817>
actor = 'JelleZijlstra'
assignee = 'none'
closed = True
closed_date = <Date 2022-02-19.01:57:22.817>
closer = 'JelleZijlstra'
components = ['Tests']
creation = <Date 2022-02-08.20:03:46.542>
creator = 'sobolevn'
dependencies = []
files = []
hgrepos = []
issue_num = 46685
keywords = ['patch']
message_count = 6.0
messages = ['412865', '412866', '412907', '412912', '412913', '413526']
nosy_count = 7.0
nosy_names = ['gvanrossum', 'JelleZijlstra', 'corona10', 'miss-islington', 'sobolevn', 'kj', 'AlexWaygood']
pr_nums = ['31222', '31223', '31229', '31230']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue46685'
versions = ['Python 3.11']

[sobolevn]

New features (like Self type and Never type), in my opinion, require some extra testing.

Things that were not covered:

• Inheritance from Self, only type(Self) is covered:

  cpython/Lib/test/test_typing.py

  Lines 193 to 196 in c018d30

  	def test_cannot_subclass(self):
  	with self.assertRaises(TypeError):
  	class C(type(Self)):
  	pass

• Equality and non-equality for Self and Never. We should be sure that NoReturn is not equal to Never, but they are equal to themselfs
• get_type_hints with Never
• get_origin with Self and Never types, it should return None for both cases
• (not exactly related) I've also noticed that this line is not covered at all:

  cpython/Lib/typing.py

  Line 725 in c018d30

  raise TypeError(f"Forward reference must be a string -- got {arg!r}")

Maybe there are some other cases?

I will send a PR :)

[JelleZijlstra]

Thanks for catching these details! Please send a PR.

[corona10]

New changeset d2d1d49 by Nikita Sobolev in branch 'main':
bpo-46685: cover TypeError of ForwardRef(1) in test_typing (GH-31223)
d2d1d49

[miss-islington]

New changeset d29bbc2 by Miss Islington (bot) in branch '3.10':
bpo-46685: cover TypeError of ForwardRef(1) in test_typing (GH-31223)
d29bbc2

[miss-islington]

New changeset bde3765 by Miss Islington (bot) in branch '3.9':
bpo-46685: cover TypeError of ForwardRef(1) in test_typing (GH-31223)
bde3765

[JelleZijlstra]

New changeset 32e3e0b by Nikita Sobolev in branch 'main':
bpo-46685: improve test coverage of Self and Never in typing (GH-31222)
32e3e0b