This is what I've actually been doing, but better to document it.

This is a slightly broader refactor than just testing. It also
consolidates information about checking type coverage/completeness.

This originates from a thread on the mypy tracker [1]. In terms of
presentation, the goal is to present guidance and offer up several
options, many of which were proposed by contributors to that thread.

Several of the goals from that thread were not achieved here,
including documentation covering stubgen and monkeytype, stubtest, and
potentially more. However, the document is written such that it should
be possible to add a section on "Generating Annotations" as was
planned earlier.

[1]: python/mypy#11506

- Add "a" to make the message grammatical
- Add a trailing period because _type_check adds another sentence after it. For example, `Unpack[3]` on 3.10 currently fails with `TypeError: Unpack accepts only single type Got 3.`.
- Use an f-string

Looks like this is in `typing.__all__` but was missed out of `typing_extensions.__all__`

Co-authored-by: Alex Waygood <[email protected]>

- Defer to the PEP 646 implementation in typing.py on 3.11
- Adjust some tests accordingly. Noted a bug in
  python/cpython#32341 (comment)
- typing._type_check() is more lenient in 3.11 and no longer rejects ints
- The representation of the empty tuple type changed

Tests pass for me on a 3.11 build from today now.