You are absolutely right! I think, I written this from instinct :D

Oh, thanks, I didn't take immutability into consideration, and created cyclic references :D

It would be really great, if Cons could be defined elsewhere (NOT in the test code). I tried to give it a somewhat cleaner skeleton, like

class Cons {
  constructor(value, next) {...}
  static fromArray(array) {...}
  filter(predicate) {...}
  map(predicate) {...}
}

but I can't do this, since Cons is already defined.

You take this to the next level m8 :)

The error messages are not really helpful. I didn't read how factorial is calculated, added the if (num <= 1) { return num; } as terminating condition, and got "1" as error message.

In my opinion, the parameter name shouldn't be rotten, since there can be healthy fruits too in that array. Just nitpicking here :)

I think I got a working implementation. When I run it, the first 3 tests run ok, then I get this message:

After pushing an 'a'
Process was terminated. It took longer than 6000ms to complete

Could the message be more specific? Or could we see, what is tested? At this point I have no idea what the test did, and where should I start fixing the implementation.