Usage of length/1 there can be performance killer. Test against [] instead as it will be much faster.

It is waste of resources to go for full 2..integer as if we know that if n divides integer then integer / n divides it as well as a / b = c <=> a / c = b. So instead of going for full range we can go up to sqrt(integer).

Another thing is that turbofish operator in collect is completely unneeded as it can be deduced by the compilator from return type.

Usage of this method is rather similar to #map than #each as we should return values returned by method not array.

No need for square brackets.

Test should use Test.assert_equal instead of Test.expect because I have receiving very helpful message: "This is not expected". I feel really sorry for coworkers of author if he write all his/her tests like this.

Of course it can. But why not use the most of rubiest ways and use already created lib for that (as it fullish all our expectations).

Why require doesn't work? I've trying to solve this using IPAddr (http://www.ruby-doc.org/stdlib-2.0.0/libdoc/ipaddr/rdoc/IPAddr.html) but it doesn't work.