Sometimes this happens no test are not bad! :)

Depends on which specs you are talking about. The description clearly state "return null". If somebody headlessly use this code somewhere else it must be their problem. If I copy code from eg. stackoverflow (argh) I always analyse the code thoroughly before running my tests.

As description states "If an attempt to divide by zero is made, return null.". Testing out of the codewars sandbox may in some cases show different results than what we see here.