adds CESU-8 encoding for encoding spec

[moofkit]

Solving #745

Encoding
Added new encoding CESU-8. Feature #15931

[eregon]

Could you move this in a separate it?
The reason is otherwise the entire spec example would fail on some Ruby implementation (reporting >= 2.7) which didn't add CESU-8 yet.
In general, ruby_version_is should be outside it blocks.

[eregon]

Maybe a better place to test this would be the Encoding.list spec or so.
Testing specific characteristics of CESU-8 (e.g., how some codepoint is encoded) would be even better.

[moofkit]

@eregon Thanks for review!

Could you move this in a separate it?

Sure!

Maybe a better place to test this would be the Encoding.list spec or so

As I see now there no tests for specific encodings in core/encoding/list_spec.rb. Maybe we should add something like that?

it 'includes CESU-8' do
  Encoding.list.include?(Encoding::CESU_8).should be_true
end

it 'includes UTF-8' do
  Encoding.list.include?(Encoding::UTF_8).should be_true
end
...
# and so on

Testing specific characteristics of CESU-8 (e.g., how some codepoint is encoded) would be even better.

Something like in Rust docs?

[eregon]

Maybe we should add something like that?

Feel free to add UTF-8 too, but I wouldn't add all the others.
CESU-8 is special in that it's a newly-added Encoding.

Yes, for instance testing 10400.chr(Encoding::CESU_8).bytes.should == [...] (from the Wikipedia example).

[moofkit]

@eregon I have added more specific specs. Can you check please?

[eregon]

Looks great, thanks for the new specs!