You are absolutely right, there is no need for this

It is creating a formated string. Here is a good video on the process:

https://www.youtube.com/watch?v=nghuHvKLhJA

That's why a kata needs random tests :)

My advice:

• complete a few hundred more katas and pay attention to them (description, test cases, etc)
• in the meantime, read the relevant documentation:
  • CW kata best practices
  • CW python test framework
  • the CW "codex"
  • python style guide
• when you're done with the reading and the katas, get started with your (first) kata

This is the first time I'm creating a kata, can you give me advice, What should I use?

It's not fair!)

No random tests

Don't use test.expect()

In the tests it looks like you're supposed to return It's an empty message! if the input is an empty string?

But this isn't mentioned in the description and it's also not tested correctly.

Error with sample tests:

Traceback (most recent call last):
  File "main.py", line 3, in <module>
    Test.assertEquals(message_cost('Hi! I`m just arrived!'), '6 r. 30 k.')
AttributeError: module 'cw-2' has no attribute 'assertEquals'