Impossible, because the test framework uses hashes for some default arguments, so the exceptions are raised during the tests. Currently, it's silent because all the overriden method are returning nil. I thought about putting a message to the console, but for the same reason, it showes itself during the test suite even for a valid solution. So... that will stay that way, unfortunately.

ah no, it's actually said at the end:

Thanks to shadchnev, I broke all of the methods from the Hash class.

it seems that the Hash class is actually overridden so that you cannot use it at all, in ruby. Meaning you're searching for another method. But that should effectively be in the description.