Ruby:

• only 1 sample test
• no random tests
• Ruby 3.0 should be enabled
• Test.assert_equals should be used instead of Test.expect

No random tests in JavaScript (at least).

BaseValue limit should to be provided in description.

Needs random tests

Also this is a duplicate of many existing katas (under the name of look-and-say numbers).

There is a flaw. You don't test any bases below 2 or above 36. The code can use the built-in string method, but it should only do so when base is between 2 and 36. Below 2 should return nil or [] or whatever else you deem fit. Above 36 would have to be implemented another way. If you only wanted to demonstrate the "clever" way, it should at least return nil when base is above 36. This way, people will see the limitations of the built-in method.