It was implemented correctly, your code just needs to check whether it has \n.

getting the same error, the tests of the creator were not well implemented

You are absolutely right.
I going to adjust my approach. Thank you.

C#: Notice the linebreak in the assertion message, Your code works incorrectly for inputs like "1234\n".

Test Failed
  Wrong output for "1234
"
  Expected: False
  But was:  True

(Resolving: Not a kata issue)

Test Failed
Wrong output for "1234"
Expected: False
But was: True

This is wrong, It should expect True not False