I'm not sure why for example :x as an argument to deconstruct_keys raises
wrong argument type Integer (expected Array) not
wrong argument type Integer (expected Array or nil)

Also wondering how to add alias for captures. Should I create file captures.rb in matchdata/shared, move there implementation of captures_spec.rb and use it with it_behaves_like?
But this alias in only for 3.2 version so not sure if its right.

Should I create file captures.rb in matchdata/shared, move there implementation of captures_spec.rb and use it with it_behaves_like?

Agree. It makes sense.

'm not sure why for example :x as an argument to deconstruct_keys raises
wrong argument type Integer (expected Array) not
wrong argument type Integer (expected Array or nil)

Looks like keys validation was changed and they check that keys is Array and elements are Symbols with Check_Type:

Check_Type(keys, T_ARRAY);
Check_Type(key, T_SYMBOL);

https://github.com/ruby/ruby/blob/master/re.c#L2425

Also I would add the following test cases:

• it returns {} when there are no named captured groups at all
• it returns {} when passed more keys than named captured groups

Thank you for the specs!