That's not my solution, that's another person solution I was testing, but random tests don't produce lists with a length equal to 9 and that solution doesn't work now.

Did you read the message after you completed the kata? There is an explanation there.

you cannot. it's permanent

You can't.

If with short test, you mean Sample tests, then you must have messed it up, this is the sample test with that input:

test.assert_equals(decode_morse('.... . -.--   .--- ..- -.. .'), 'HEY JUDE')

And as you can see, the three spaces are there. Backup you code, click reset and paste it again. When reporting a problem, mention the language you're using, I assumed it's Python.

First come the solutions who have received positive votes, then the other submitted solutions, the later the first. That's why your solution appears like the first one after the voted ones. New solutions will come above yours, unless it receives a positive vote.

"with out" ??
It doesn't use any reverse list

If the requested string length is smaller than or equal to 3 characters, then the length of the dots is not added to the string length.

e.g. trim("He", 1) should return "H...", because 1 <= 3

It's already there and with an example. What is it that confuses you?