Not a kata issue, those brackets aren't part of the input (print it). That's JUnit way of highlighting where two strings differ.

the inputs should be only letters and spaces, but I get this:
expected:<...cXva RiVmo tMo HYPYu[ ]> but was:<...cXva RiVmo tMo HYPYu[]>

Any (real) number squared is a positive number. 14^2 === -14^2.

If you want to see the input, you have to print the input, not the output...

A mi me sale el mismo error al final resolviste cual era el problema

Alguien sabe que validacion en el codigo hace el test4 porque es el unico que me falta para pasar este reto

I suppose you did not read the correct output. Moreover you passed the kata. You should read other solutions.

On the right side (b), I don't see -14. a can be negative.