This is the best solution and if you have something to tell shut up please ;)

added in JavaScript. already existing in Haskell

fixed

the real Clever is removing the const keyword from the arguments

The test is trying to use the + operator to add two integer arrays. You are responsible for implementing this functionality. The error message means that you haven't achieved that.

There might be an issue with the Kata's tests. I'm getting the following error after submission, although I don't have array + array operation.
The stack trace is:

An error occurred while loading ./spec/query_spec.rb.
Failure/Error: actual = DB[actual].to_a if actual.is_a?(String)

Sequel::DatabaseError:
  PG::UndefinedFunction: ERROR:  operator does not exist: integer[] + integer[]
  LINE 1: SELECT id, a, b, c, a + b AS "a + b", (a + b) + c AS "(a + b...
                                ^
  HINT:  No operator matches the given name and argument types. You might need to add explicit type casts.
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:156:in `exec'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:156:in `block in execute_query'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/database/logging.rb:38:in `log_connection_yield'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:156:in `execute_query'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:144:in `block in execute'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:120:in `check_disconnect_errors'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:144:in `execute'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:500:in `_execute'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:318:in `block (2 levels) in execute'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:522:in `check_database_errors'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:318:in `block in execute'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/connection_pool/threaded.rb:92:in `hold'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/database/connecting.rb:269:in `synchronize'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:318:in `execute'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/dataset/actions.rb:1093:in `execute'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:614:in `fetch_rows'
# /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/dataset/actions.rb:152:in `each'
# ./spec/support/preloaded.rb:11:in `to_a'
# ./spec/support/preloaded.rb:11:in `compare'
# ./spec/query_spec.rb:18:in `block in <top (required)>'
# ./spec/query_spec.rb:14:in `<top (required)>'
# ------------------
# --- Caused by: ---
# PG::UndefinedFunction:
#   ERROR:  operator does not exist: integer[] + integer[]
#   LINE 1: SELECT id, a, b, c, a + b AS "a + b", (a + b) + c AS "(a + b...
#                                 ^
#   HINT:  No operator matches the given name and argument types. You might need to add explicit type casts.
#   /usr/local/bundle/gems/sequel-5.47.0/lib/sequel/adapters/postgres.rb:156:in `exec'
No examples found.

It seems for testing the column a + b AS "a + b" is used.

magic outside of hogwarts

is doesn't work the same way as == for non-primitive types.

added + chai assertions + removed non-integer inputs

Fixed in this fork

Thank you. Minifing was really challanging part!

Hm... The first simple tests run quickly. And then everything freezes, followed by a timeout. Is there something wrong with the tests?..

I solved this problem in Java. Now I have implemented the same algorithm line by line in Python. But the program does not pass the checks on large tests... And on some of them it works.

I don't understand what's happening in line 3. TT

That's not an issue I think. Many katas have 'bonus point' followups that are now actually required.