var random = Math.random(); // Can not be guessed

Well, about that

• assertSimilar is deprecated, use assertDeepEquals
• I read this as first sort alphabetically, than by length desc, but it's ofcourse the other way around The boggleSolver function must return an array of all found words, sorted alphabetically by length descending.

It's created as a property of lexicalEnvironment object of function. This object is hidden. We don't have access to that object directly.
ECMAScript® 2020 Language Specification => 8.1 Lexical Environments

so it's the same task, with one more outer loop... ;p

I don't think it is a duplicate, though. In the other kata you're supposed to check if one word is valid; in this one, you're searching the entire board for all words matches in an array of words and returning all words you find in the given board.

I'm mostly opening issues to old katas to prevent others from accidentally approving it (it's approvable, obviously).

I guess you can keep one issue around and close the other if you want.

This kata predates its duplicate by about two years ( which probably explains the lack of random tests ). Also, author is long gone, so it's probably not going to be unpublished.

Would it be reasonable to close this issue?

Needs random tests

A duplicate of https://www.codewars.com/kata/boggle-word-checker

Great kata! Thanks. :-)

What keeps getSecret from being called on createSecretHolder's invocation?

Done!

+1 lkcelaks
[[]] The special case [[]] should be explicit in the kata description