Sample tests should include case where numbers are diffent, but they're both either odd or even.
For instance Ruby:
Test.assert_equals(lovefunc(7,5), false)
or
Test.assert_equals(lovefunc(6,8), false)

Sample tests are passable with simple "value1 != value2", although they obviously fails the attempt and they would also fail if any of two examples above would be added.

If the score < 0, return 0

Ah, I never seen on CodeWars sample tests that wouldn't work, so somehow I didn't even dare to attempt without passing sample tests, but my code of course worked when I used it to pass the challenge.

This kata does not have Sample Tests in Ruby. There is an issue posted about this. There is just some boilerplate code instead.

I didn't use method "add" in my code so why am I getting error "undefined methord add"?

that's from your own code though?

It seems like tests in Ruby are not working correctly? My code works in REPL(IRB) and I checked Ruby documentation for 2.5.0 that includes code I've used. So following error message seems to come from incorrect tests - "undefined method 'add'"?

#<NoMethodError: undefined method add' for main:Object> main.rb:12:in block (2 levels) in '
/runner/frameworks/ruby/cw-2.rb:180:in wrap_error' /runner/frameworks/ruby/cw-2.rb:72:in it'
/runner/frameworks/ruby/cw-2.rb:206:in it' main.rb:11:in block in '
/runner/frameworks/ruby/cw-2.rb:55:in block in describe' /runner/frameworks/ruby/cw-2.rb:46:in measure'
/runner/frameworks/ruby/cw-2.rb:51:in describe' /runner/frameworks/ruby/cw-2.rb:202:in describe'
main.rb:10:in `'